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Composite Structures
Journal Prestige (SJR): 1.905
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  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 0263-8223 - ISSN (Online) 0263-8223
Published by Elsevier Homepage  [3206 journals]
  • A general property-structure relationship from crack stability analysis on
           hybrid staggered composites with elasto-plastic matrices
    • Abstract: Publication date: Available online 17 February 2020Source: Composite StructuresAuthor(s): Zhongliang Yu, Junjie Liu, Xiaoding WeiAbstractIn the present study, fracture analysis is carried out on the representative unit cell of staggered composites consisting of hybrid reinforcements and elasto-plastic matrices. The deformation and failure of hybrid composites are examined through energy-based fracture theory. Analytical formulae for characteristic overlap length, failure strain, and toughness of the unit cell that are related to the properties and geometries of constituents emerge from rigorous derivations. The influences of the matrix plasticity and tablet dissimilarity on the crack stability, the characteristic overlap length, the final failure strain, and toughness are also elucidated. Our study shows that if designed appropriately, the matrix plasticity can effectively improve the material ductility and toughness through crack stabilization. On the other hand, although hybrid reinforcements could effectively tune the ductility, they may cause a loss of material toughness in some cases. More importantly, our model provides guidance to the promising design space where the well-known ductility-strength trade-off dilemma for traditional engineering materials could be resolved.
  • Prediction of Residual Mechanical Properties in Flexure-After-Impact of
           Woven Composite Beams through Electrical Resistance Measurement
    • Abstract: Publication date: Available online 17 February 2020Source: Composite StructuresAuthor(s): Xiaoying Cheng, Yi Gong, Yisheng Liu, Zhenyu Wu, Xudong HuAbstractLow-velocity impact and flexure-after-impact (FAI) tests were performed on 2D plain woven fabric (PWF) and 3D orthogonal woven fabric (OWF) reinforced carbon fibers/epoxy composite beams while the electrical resistance measurement was applied during impact and FAI tests via four-probe technique to study the relations between resistance variation (RV) and residual mechanical properties. The impact tests (from 3J to 9J) showed that OWF specimens have better suppression of delamination than PWF, which was also evaluated through thermography and cross-sectional imaging method. Then FAI tests were implemented on impacted specimens while acoustic emission signals were captured. The residual flexural strength and modulus from the FAI tests were normalized by the values of intact specimens and compared with the RV from impact tests. The relations between electrical and mechanical properties revealed that the rise of resistance after the impact is an effective sign that indicates the reduction in the residual flexural strength and modulus of the composite beam. Moreover, the relation between RV and residual modulus is more effective than that with residual strength.
  • Constructing a simple anti-sandwich structure on carbon fiber surface for
           simultaneously strengthening and toughening the interphase of epoxy
    • Abstract: Publication date: Available online 17 February 2020Source: Composite StructuresAuthor(s): Qing Wu, Jinqian He, Fen Wang, Xin Yang, Jianfeng ZhuAbstractA simple anti-sandwich structure that employs strong, stiff and tough graphene oxide as the core layer, flexible polyether amine as the wrapping connection faces is constructed on carbon fiber surface via chemical grafting approach to strengthen and toughen the interphase of epoxy composites. Impressive 94.4% and 48.7% increments in interfacial toughness and interfacial shear strength are achieved in composites with anti-sandwich structure on fiber, by analogy to those of untreated fiber composites. Pertinent strengthening reasons are mainly enhanced surface energy and the hybrid molecular entanglement. Probable toughening mechanisms include crack deflection by GO core layer, appropriate chemical bonds at interphase, plastic deformation of polyether amine and interfacial friction between adjacent layers due to the build of anti-sandwich structure, as well as the localized toughening effect of the matrix. This work provides a promising thought to obtain advanced composites with excellent strength and toughness.
  • Closed-form formulae for prediction of homogenized ply-properties and
           laminate thermo-elastic constants in symmetric laminates containing ply
           cracks in multiple orientations
    • Abstract: Publication date: Available online 17 February 2020Source: Composite StructuresAuthor(s): H. Ahmadi, M. Hajikazemi, W. Van PaepegemAbstractThe aim of this study is to develop a novel model for predicting homogenized properties of a cracked ply in a symmetric laminate using the crack density and thickness of the ply. In doing so, the periodic boundary conditions are applied to the RVEs in a three-dimensional finite element model to calculate the thermo-elastic constants of symmetric laminates containing uniformly and non-uniformly spaced cracks under in-plane and out-of-plane loading conditions. On the other hand, homogenized material properties of the cracked ply are explicitly determined by averaging procedures for both stress and strain components. Using computed results and nonlinear least square fitting, an analytical formula is proposed to describe the mechanical properties of the cracked ply, which takes into account the effect of ply thickness, material properties, and crack density. Different cracked laminates are tested to indicate the potential of the developed method in analyzing complex crack geometries in multiple orientations. Moreover, the applicability and accuracy of the suggested model are verified by comparing the results with those of experiments, variational approach and finite element method.
  • Development of composite double-hat energy absorber device subjected to
           traverser loads
    • Abstract: Publication date: Available online 15 February 2020Source: Composite StructuresAuthor(s): F. Alkhatib, E. Mahdi, A. DeanAbstractThis paper introduces a new carbon fiber reinforced plastic (CFRP) structural system in the field of crashworthiness. CFRP hat-shaped and angle-shaped stiffeners were used to develop a double-hat collapsible energy absorption system. Three different design alternatives were investigated. The first alternative is an open-cell design (OC) consisting of two flipped hat stiffeners with four right angles on the edges. The second alternative is a one-in-cell double-hat design (1C), consisting of OC design with additional one inside small hat stiffeners edged with angles. The third alternative is a two-in-cell double-hat design (2C), consisting of OC design with additional two inside small hat stiffeners edged with angles. Three modes of failure were observed, classified as local buckling (mode I), top wall bending (mode II), and brittle collapse that resulted from Euler buckling (mode III). The crashworthiness characteristics were evaluated for the three designs. The 2C double-hat design showed the highest peak load and specific energy absorption (SEA). Accordingly, the core of the 2C design was filled with foam to increase the energy absorption capability and enhance the structure’s stability. Results showed that the SEA of the 2C+ foam design was increased by more than 50% compared to the coreless 2C double-hat design.
  • Two-Scale Asymptotic Expansion Method for Periodic Composite Euler Beam
    • Abstract: Publication date: Available online 15 February 2020Source: Composite StructuresAuthor(s): Z.W. Huang, Y.F. Xing, Y.H. GaoAbstractThis paper develops a two-scale asymptotic expansion solution method for periodic composite Euler beam for the first time. In this method, a two-scale solution in the asymptotic expansion form is achieved for the fourth-order uniformly elliptic differential equation with periodic oscillating coefficients, and it shows the first-order perturbed displacement is zero in this solution. The analytical solutions of the unit cell problem are found with the help of four normalization conditions proposed in this work, and it follows that the homogenized elastic modulus of periodic composite beam is exactly the harmonic mean of material moduli. Another contribution of this work is to mathematically verify the convergence of the two-scale asymptotic expansion solution through the two-scale convergence method. In addition, the paper reveals the effects of higher-order expansion terms on the two-scale displacements and concludes that the second order or even higher-order perturbed displacements are necessary for obtaining accurate curvatures relevant to micro stress. Finally, numerical experiments validate that the present method is rigorous in mathematics and physically acceptable.
  • 3/2 superharmonic resonance and 1/2 subharmonic resonance of functionally
           graded carbon nanotube reinforced composite beams
    • Abstract: Publication date: Available online 14 February 2020Source: Composite StructuresAuthor(s): Zhihua Wu, Yimin Zhang, Guo YaoAbstractThis paper deals with the 3/2 superharmonic resonance and 1/2 subharmonic resonance of functionally graded carbon nanotube reinforced composite (FG-CNTRC) beams. In the framework of Timoshenko beam theory and von Kármán type of geometric nonlinearity, the nonlinear equations of motion for FG-CNTRC beams are derived by Hamilton’s principle and discretized by the Galerkin method. The incremental harmonic balance (IHB) method is used to calculate the dynamic responses of FG-CNTRC beams subjected to transverse harmonic excitation. The stability of steady state solutions obtained from the IHB method is evaluated by Floquet theory. It is found that when the period-1 solutions of FG-CNTRC beams with asymmetric carbon nanotube distribution lose stabilities and the period doubling bifurcation occurs, the nonlinear system will generate 3/2 superharmonic resonance and 1/2 subharmonic resonance respectively in two specified frequency ratio intervals. The frequency response curves of 3/2 superharmonic resonance and 1/2 subharmonic resonance are constructed by the IHB method. The numerical results reveal the effects of material, geometry and excitation parameters on the 3/2 superharmonic and 1/2 subharmonic resonant responses of the system. Additionally, the two unstable regions where the 3/2 superharmonic and 1/2 subharmonic resonances occur are determined under different parameters.
  • A three-dimensional hierarchic finite element-based computational
           framework for the analysis of composite laminates
    • Abstract: Publication date: 1 May 2020Source: Composite Structures, Volume 239Author(s): Z. Ullah, Ł. Kaczmarczyk, C.J. PearceAbstractA three-dimensional hierarchic finite element-based computational framework is developed for the investigation of inter-laminar stresses and displacements in composite laminates of finite width. As compared to the standard finite elements, hierarchic finite elements allow to change the order of approximation both locally and globally without modifying the underlying finite element mesh leading to very accurate results for relatively coarse meshes. In this paper, both symmetric cross-ply and angle-ply laminates subjected to uniaxial tension are considered as test cases. Tetrahedral elements are used for the discretisation of laminates and uniform or global p-refinement is used to increase the order of approximation. Each ply within laminates is modelled as a linear-elastic, homogenous and orthotropic material. With increasing the order of approximation, the developed computational framework is able to capture the complex profiles of inter-laminar stresses and displacements very accurately. Results are compared with reference results from the literature and found in a very good agreement. The computational model is implemented in our in-house finite element software library Mesh-Oriented Finite Element Method (MoFEM). The computational framework has additional flexibly of high-performance computing and makes use of the state-of-the-art computational libraries including Portable, Extensible Toolkit for Scientific Computation (PETSc) and the Mesh-Oriented datABase (MOAB).
  • Stress redistribution around fiber breaks in unidirectional steel fiber
           composites considering the nonlinear material behavior
    • Abstract: Publication date: 1 May 2020Source: Composite Structures, Volume 239Author(s): Baris Sabuncuoglu, Caglar Mutlu, F. Suat Kadioglu, Yentl SwolfsAbstractThe use of steel fibers as reinforcement in polymer composites is recently increasing thanks to their ductility, high stiffness and wide range of diameters. Unlike carbon and glass fibers, steel fibers often end up with a non-circular cross-section due to their manufacturing technology. This may influence the stress redistribution around fiber breaks, which is important in longitudinal tensile failure of unidirectional composites. A parametric study was performed by using 3D finite element models with randomly distributed and oriented hexagonal fibers. Rather than the fiber shape, the distance between fibers was shown to have an influence on stress concentrations in terms of both average and peak stress concentrations. The plastic behavior of steel fibers resulted in smaller stress concentrations and faster stress recovery whereas the opposite was observed for the plastic behavior of epoxy. For different strain levels, results were shown to depend on the relative stiffness of steel and epoxy in the plastic region.
  • Quasi-static bending and transverse crushing behaviors for hat-shaped
           composite tubes made of CFRP, GFRP and their hybrid structures
    • Abstract: Publication date: 1 May 2020Source: Composite Structures, Volume 239Author(s): Dongdong Chen, Guangyong Sun, Xihong Jin, Qing LiAbstractThis study aims to characterize the crushing responses of hat-shaped composite tube under quasi-static three-point bending (TPB) and transverse compression (TC) conditions. The specimens were fabricated with different stacking configurations considering the effect of ply number, ply angle (containing [±45°] layers) and interply hybrid structure (sandwich-like) with carbon fiber reinforced plastic (CFRP) and glass fiber reinforced plastic (GFRP) through thermo-forming process. Mechanical parameters were also tested with non-hybrid laminates consisted of net carbon and net glass fibers. The crushing performance was evaluated by comparing load-displacement curves and the images taken in course of the testing processes. Cross-sections of the specimens were also inspected visually to identify the failure mechanisms after the tests. The comparative study on the energy absorption and cost efficiency was conducted for all the samples. It was found that failure modes varied with ply angle under the TPB tests but kept the same under the TC tests. Increasing wall thickness seemed to be an effective way to improve energy absorption under both TPB and TC loading. Addition of [±45°] layers exhibited considerable advantages on the TPB performance except the TC scenario. The hybrid structures comprised of both carbon and glass fiber layers exhibited limited improvement on crashworthiness but excellent cost efficiency. In addition, the initiation and propagation of cracks during tests were clearly visible when stacking glass fiber layers outside, which facilitate proper structural health monitoring.
  • Effect of heterogeneity on crushing failure of disordered staggered-square
    • Abstract: Publication date: Available online 14 February 2020Source: Composite StructuresAuthor(s): Deepak Kumar, Anuradha BanerjeeAbstractUni-axial compressive failure of silica-epoxy based heterogeneous honeycombs is investigated in detail for a range of volume fractions. Introduction of heterogeneity in compression of staggered-square honeycomb is seen to result in damage initiation at multiple locations and subsequent damage growth to be more stable compared to pure epoxy in which damage was observed to be localized until peak load when catastrophic failure of the honeycomb specimen occurs. The increase in stiffness and comparative stability of the response is accompanied with reduction in strength, however, between 0-5% the total work of compressive failure is comparable. From the elastic-plastic analysis it is evident that the non-linearity in the response of pure honeycombs, prior to peak load, is largely due to formation of plastic hinges near corners of cells, whereas in case of heterogeneous honeycomb the non-linearity is mostly due to debonding of hard filler particles and matrix cracking leading to damage growth in cell walls.
  • Mechanical properties of SiCp/SiC composite lattice core sandwich panels
           fabricated by 3D printing combined with precursor impregnation and
    • Abstract: Publication date: Available online 13 February 2020Source: Composite StructuresAuthor(s): Kun Zhang, Tao Zeng, Guodong Xu, Su Cheng, Siwen YuAbstractSilicon carbide particle/silicon carbide (SiCp/SiC) composite lattice core sandwich panels were fabricated by selective laser sintering (SLS) combined with precursor impregnation and pyrolysis (PIP) process. The compression properties of the SiCp/SiC composite lattice core sandwich panels with three different configurations under room temperature and high temperature were investigated. The room temperature experiment results were compared with the analytical predictions. Experiment results indicated that the compression strength and modulus decreased 34.30% and 44.82% as the temperature increased from 1400℃ to 1800℃. Moreover, the failure mechanisms of the SiCp/SiC composites were analyzed.
  • Explicit neural network model for predicting FRP-concrete interfacial bond
           strength based on a large database
    • Abstract: Publication date: Available online 12 February 2020Source: Composite StructuresAuthor(s): Yingwu Zhou, Songbin Zheng, Zhenyu Huang, Lili Sui, Yang ChenAbstractThis study builds a large database from an extensive survey of existing single-lap shear tests on fiber-reinforced polymer (FRP)-concrete interfacial bonds, comprising 969 test results. Twenty shear-bond strength models published over the past 20 years have been collected and analyzed. These models take into account the effects of the concrete compressive strength, concrete width, FRP elastic modulus, FRP thickness, FRP width and FRP bond length on the ultimate bond strength of the FRP-concrete interface. This paper evaluates the predictive accuracy of the 20 collected models and finds that these models have limited accuracy. To accurately predict the bond strength of the FRP-concrete interface, this paper employs the back propagation neural networks (BPNN) method to train and test the database and builds an artificial neural networks (ANN) model that consists of weighted values, biases and transfer functions. The ANN model test conducts 84 training iterations and selects the optimal combination of input nodes. The accuracy of the developed ANN model is higher (i.e., lower predictive error) than that of the existing bond strength models in the literature. Furthermore, this paper develops an explicit user-friendly formula based on the trained ANN model. The proposed formula estimates and validates the 969 bond strength results, and the predictions using the explicit equation fit the test data very well with small error. As such, the formula can be easily applied during practical designs instead of the implicit processes in the ANN model.
  • A structured method to generate conformal FE mesh for realistic textile
           composite micro-geometry
    • Abstract: Publication date: Available online 11 February 2020Source: Composite StructuresAuthor(s): Agniprobho Mazumder, Youqi Wang, Chian-Fong YenAbstractA procedure is developed to generate a conformal finite element mesh of a textile composite unit cell with a complex micro-geometry with the aim of improving the accuracy of micro-mechanics analysis. A realistic micro-geometry of a textile composite unit cell is initially generated by using a fiber level dynamic relaxation approach. Yarn surfaces are then discretized into triangle elements. An algorithm is established to remove inter-yarn interferences and gaps induced by numerical errors. The unit cell is first divided into a uniform cuboid element mesh, which is later modified and converted to a conformal finite element (FE) mesh through of a process of node shifting and element splitting. In the conformal mesh, the element boundary perfectly matches the yarn-to-yarn interface. Compatibility between elements is ensured. The quality of each element is examined. The mesh can be input to commercial FEM softwares for composite stress analysis.
  • Study on the flexural strengthening effect of RC beams reinforced by FRP
           grid with PCM shotcrete
    • Abstract: Publication date: Available online 30 January 2020Source: Composite StructuresAuthor(s): Rui Guo, Wenhao Hu, Mengqi Li, Shinichi HinoAbstractRecently a new repair and retrofit method of reinforced concrete (RC) members that uses fibre-reinforced-polymer (FRP) grid with polymer-cement-mortar (PCM) shotcrete has been proposed. Four RC beams externally strengthened with CFRP grid-PCM at the bottom and one non-reinforced RC beam were tested to reveal their flexural behaviour and strengthening effect. The number of FRP layers and reinforcement amount per unit length of the CFRP grid were selected as the two main parameters in the test programme. The test results indicated that the flexural strengthening effect of the CFRP grid-PCM was sufficient; moreover, two-layer reinforcements were effective as one-layer ones under similar unit-reinforcement values. Furthermore, a new analytical model was proposed to evaluate the flexural capacities of RC beams strengthened with CFRP grid, and the predicted values were well matched to the test results and collected data.
  • Optimization of hybrid natural laminated composite beams for a minimum
           weight and cost design
    • Abstract: Publication date: Available online 23 January 2020Source: Composite StructuresAuthor(s): M. Megahed, Rasha M. Abo-bakr, S.A. MohamedAbstractIn recent years, the use of bio-fibers to replace synthetic fibers in composites has gained popularity due to increasing environmental concerns and requirements for developing sustainable materials for engineering applications. The objective of this study is to minimize the weight and cost of a symmetric laminated composite beam with a specified lower bound constraint on its natural frequency. The optimal design of hybrid composite beams with different boundary conditions was considered. The optimization problem accounts for fiber type, fiber volume fractions, thickness, and fiber orientation angles of different layers as design variables. The optimum design of the hybrid carbon/flax/epoxy laminated beam for different values of frequency lower limits was computed and compared with those of the hybrid carbon/glass/epoxy, neat glass/epoxy, and neat flax/epoxy laminated beams. Results showed that hybridization between the carbon fiber and flax fiber results in the best designs with the advantages of a lightweight, low cost and higher fundamental frequencies.
  • Modal analysis of a Variable Stiffness Composite Laminated plate with
           diverse boundary conditions: Experiments and modelling
    • Abstract: Publication date: 1 May 2020Source: Composite Structures, Volume 239Author(s): Ana Margarida Antunes, Pedro Ribeiro, José Dias Rodrigues, Hamed AkhavanAbstractThe modes of vibration of a Variable Stiffness Composite Laminate were obtained by experimental modal analysis and compared with the ones resulting from theoretical/mathematical models. Three types of boundary condition were considered: CFFF, CFCF and FFFF, where C stands for clamped and F for free edges. Frequency response functions were experimentally obtained and employed to identify natural frequencies, modal damping ratios and mode shapes of vibration, using methods known as CMIF - Peak picking and circle-fit. The identified natural frequencies and mode shapes of vibration were compared with the ones resulting from models based on Classical Plate Theory and on First-order Shear Deformation Theory. Although two massive, stiff, steel blocks were bolted with the plate in-between in order to approach a clamped boundary, the modal properties are still significantly influenced by the flexibility of the resulting fixture. After introducing springs along the boundaries in the mathematical model, to better represent a “real clamped” boundary, quite good agreement between theoretical and experimental results was obtained. The experimental results here presented can be used to validate theoretical models of Variable Stiffness Composite Laminated plates.
  • Variational analysis of cracking in general composite laminates subject to
           triaxial and bending loads
    • Abstract: Publication date: 1 May 2020Source: Composite Structures, Volume 239Author(s): M. Hajikazemi, L.N. McCartney, H. Ahmadi, W. Van PaepegemAbstractA robust variational approach is first developed for predicting stress/displacement fields and effective thermo-elastic constants in a laminate with arbitrary lay-up, containing uniformly spaced ply cracks, subject to general triaxial and bending loads when the effects of thermal residual stresses are also considered. The methodology extends some previously developed variational approaches so that general non-symmetric lay-ups (not only cross-ply) under through-thickness loading conditions can be analyzed. Secondly, an approximate methodology is introduced which enables the approach to predict all effective thermo-elastic constants of laminates having non-uniformly spaced ply cracks, including new types of constant required to account for out-of-plane loading. Thirdly, some novel inter-relationships among effective thermo-elastic constants of cracked and uncracked general laminates are obtained showing that just three macroscopic parameters define the dependence of all relevant laminate constants (thirty five) on the state of cracking. The results are compared with those obtained from finite element methods, experiments and other high accuracy models.
  • Review of recent developments and induced damage assessment in the
           modelling of the machining of long fibre reinforced polymer composites
    • Abstract: Publication date: Available online 10 February 2020Source: Composite StructuresAuthor(s): F. Cepero-Mejías, J.L. Curiel-Sosa, A. Blázquez, T.T. Yu, K. Kerrigan, V.A. PhadnisAbstractThis manuscript offers a comprehensive review of the state of art on the machining induced damage modelling of long fibre reinforced polymers (LFRP), focusing on the two most common simulated machining operations, orthogonal cutting and drilling. A novel and critical discussion of composite damage modelling techniques used in machining works is ofered, yielding numerous insights; advantages and disadvantages of current numerical techniques as well as possible improvements are included. Additionally, computational findings achieved so far in the literature are analysed in detail to allow remark of the current scope in the machining of LFRP laminates. Despite ingenious numerical solutions having been generated by previous authors to face the complex problems involve with the simulation of composite machining, the numerical capabilities to model the machining induced damage are still limited. Hence, different numerical strategies should be considered in future computational studies to enhance the reliability of current finite element models. The use of advanced continuum damage mechanics (CDM) approaches inserted via user-defined subroutines or the use of other computationally advanced methods such as eXtended Finite Element Method (XFEM) or phase field methods (PFM) to model composite fracture are recommended to improve the quality of numerical predictions.
  • Modelling of a GFRP adhesive connection by an imperfect soft interface
           model with initial damage
    • Abstract: Publication date: Available online 10 February 2020Source: Composite StructuresAuthor(s): A. Maurel-Pantel, M. Lamberti, M.L. Raffa, C. Suarez, F. Ascione, F. LebonAbstractIn this paper a methodology to model a GFRP adhesive connections by using an imperfect soft interface model is presented. The model based on Kachanov’s theory considered a cracked thin adhesive. Within this framework, the mechanical properties and the initial damage (diffuse initial cracks) of the adhesive layer has been experimentally evaluated. With a modified Arcan system, static tests were performed on adhesively bonded assemblies in tensile and shear solicitation mode considering three different adhesive thicknesses. The experimental results highlighted how the thickness of adhesive influences the mechanical strength and stiffness of the bonded connection. CT-scans were performed to measure the porosity rate in the adhesive layer. Furthermore, the excellent comparison of numerical and experimental data of an adhesive GFRP bonded connections allow us to consider the imperfect soft interface model proposed as highly competitive to evaluate complex structure performance in civil engineering context. A parametric analysis has been proposed to provide a formula able to describe the full response of the structure at varying adhesive property.
  • The multi-physic cell-based smoothed finite element method for dynamic
           characterization of magneto-electro-elastic structures under thermal
    • Abstract: Publication date: Available online 10 February 2020Source: Composite StructuresAuthor(s): Liming Zhou, Ming Li, Yan Cai, Hongwei Zhao, Erfei ZhaoAbstractThis study was aimed to computationally investigate the thermal load combining the mechanical load effect on dynamic characteristics of intelligent composite structures. For this purpose, the cell-based smoothed finite element method (CS-FEM) was applied to the multi-physic coupling problem, and the coupled multi-physic CS-FEM (CPCS-FEM) integrating the magneto-electro-thermo-elastic (METE) coupling effect was put forward. Compared with standard FEM, this method with higher accuracy, lower mesh restriction and much less calculation for stochastic issues was more capable in handling severe mesh distortion and deformation. The convergence, accuracy and efficiency of CPCS-FEM were validated with three numerical cases. With CPCS-FEM integrating the modified Newmark scheme, the thermal effects on generalized displacement (x- and z-direction displacement components, electric and magnetic potentials) of magneto-electro-elastic sensors were explored. This study presents an effective approach to model the complicated multi-physic problem, and the simulation findings contribute to the design of intelligent structures in service under thermal conditions.
  • Large amplitude vibration of functionally graded graphene nanocomposite
           annular plates in thermal environments
    • Abstract: Publication date: Available online 8 February 2020Source: Composite StructuresAuthor(s): Helong Wu, Jun Zhu, Sritawat Kitipornchai, Quan Wang, Liao-Liang Ke, Jie YangAbstractThis paper investigates the large amplitude vibration of functionally graded nanocomposite multilayer annular plates reinforced with graphene platelets (GPLs) in thermal environments. It is assumed that the GPL concentration varies from layer to layer across the plate thickness but remains constant in each individual GPL-reinforced composite (GPLRC) layer, whose elastic modulus is estimated by the modified Halpin-Tsai micromechanics model. Within the framework of first-order shear deformation theory and von Kármán geometric nonlinearity, the governing equations are derived by using the Hamilton’s principle and then solve by the differential quadrature method together with an iterative scheme. Numerical results are presented to show the influences of GPL geometry, distribution pattern and concentration, plate geometry, boundary conditions, as well as temperature rise on the nonlinear vibration behaviour of functionally graded GPLRC annular plates. It is found that dispersing more GPLs within the outer layers substantially decreases the nonlinear frequency ratio, while the effect of GPL geometry is insignificant.
  • On frequency response of porous functionally graded
           magneto-electro-elastic circular and annular plates with different
           electro-magnetic conditions using HSDT
    • Abstract: Publication date: Available online 8 February 2020Source: Composite StructuresAuthor(s): M VinyasAbstractIn this article, the vibrational behaviour of porous functionally graded magneto-electro-elastic (P-FGMEE) circular and annular plates is explored through finite element procedures. The influence of different electro-magnetic boundary conditions on the coupled natural frequencies of P-FGMEE plates are evaluated for the first time. The governing equations are arrived through Hamilton’s principle under the framework of higher order shear deformation theory (HSDT) in polar coordinates. The magneto-electro-elastic (MEE) material properties are assumed to vary along the thickness based on power-law model. The proposed model is verified for its correctness with previously published literature and also with numerical software. In addition, the effects of various prominent parameters such as gradient index, porosity volume, functionally graded pattern, diameter ratio, coupling fields etc., on the frequency response of P-FGMEE circular and annular pates are also discussed. The results of this article can be effectively incorporated for the accurate design and development of functionally graded smart structures with porosities.
  • A double porosity material for low frequency sound absorption
    • Abstract: Publication date: 1 May 2020Source: Composite Structures, Volume 239Author(s): Honggang Zhao, Yang Wang, Dianlong Yu, Haibin Yang, Jie Zhong, Fei Wu, Jihong WenAbstractThis work designs a double porosity material (DPM) composed of two types of pores, i.e., the micro-pore from the porous layer and the meso-pore made by the labyrinthine channel. The both loss mechanisms of two different pores are combined to explore the low frequency sound absorption. All theoretical, numerical and experimental results show that the DPM possesses much lower frequency sound absorption than that of homogenous porous material (HPM) under the same thickness. Both the pressure and particle velocity distributions reveal that the sound absorption peaks are induced by the resonances of the labyrinthine channel and the hybrid resonance between the porous layer and labyrinthine channel respectively. Moreover, unconventional features such as negative bulk modulus and slow sound speed are observed around the resonant frequencies of the DPM. Finally, the absorption tailoring of the DPM with different strategies is investigated.
  • Cyclic shear behavior of masonry walls strengthened with prestressed steel
           bars and glass fiber grids
    • Abstract: Publication date: 15 April 2020Source: Composite Structures, Volume 238Author(s): Keun–Hyeok Yang, Ju–Hyun Mun, Seung–Hyeon HwangAbstractThe present study developed a new and original strengthening method to enhance the shear capacity and ductility of unreinforced masonry (URM) walls based on the unbonded prestressed units using steel bars and glass fiber (GF) grids. The strengthening efficiency was validated through the experimental analyses including the failure mode, the lateral load-displacement relationship, shear capacity, and work damage indicator measured from four specimens subjected to a constant axial load and cyclic lateral loads. In addition, new design equations for the shear capacity of masonry walls were derived based on the regression analysis of 172 datasets. In particular, the proposed equations considered the shear enhancement by the axial stresses created due to the prestressed strengthening materials. The test results showed that shear capacity of the masonry walls strengthened with diagonal steel bars and GF grids increased by 4.2 times when compared with that of the companion URM walls. The proposed design equations for shear capacity of masonry walls also exhibited superior accuracy to FEMA 306 and EC 6 models.
  • Determination of in-plane and through-the-thickness coefficients of
           thermal expansion in composite angle brackets using digital image
    • Abstract: Publication date: 15 April 2020Source: Composite Structures, Volume 238Author(s): Enrique Graciani, Jesús Justo, Patricia Lucía ZumaqueroAbstractA procedure for the simultaneous determination of in-plane and through-the-thickness coefficients of thermal expansion (CTEs) in composite angle brackets is presented. Carbon fibre/epoxy samples are heated and digital image correlation is used to determine the in-plane strains and out-of-plane displacements in one side of each sample. In-plane CTEs are obtained from the average in-plane strains measured at different temperatures. Through-the-thickness CTE is obtained from the angular distortion of the samples at different temperatures, which is determined from the out-of-plane displacements. One quasi-isotropic and two unidirectional samples are used. Unidirectional samples allow the material’s in-plane CTEs in orthotropic directions to be determined. Material’s in-plane CTEs permit predicting an in-plane CTE value for the quasi-isotropic sample that agrees with the experimental measurements. Conversely, results obtained for the through-the-thickness CTE in all samples show a significant dispersion. This fact is attributed to the manufacturing distortions present in the curved part of the samples.
  • Linear damage localization in CFRP laminates using one single fiber-optic
           Bragg grating acoustic emission sensor
    • Abstract: Publication date: 15 April 2020Source: Composite Structures, Volume 238Author(s): Fengming Yu, Yoji OkabeAbstractHighly sensitive ultrasonic fiber-optic Bragg gratings (FBGs) have been used as acoustic emission (AE) sensors in the non-destructive inspection (NDI) for analyzing damage progression during the material tests of carbon fiber reinforced plastic (CFRP) laminates. Localization of the damage-induced AE source is one of the desirable functions for enhancing the efficiency of the AE-based NDI method. Hence, we attempted to establish a linear source localization method in a coupon-shaped CFRP test specimen with a highly sensitive FBG sensor. In particular, to protect the FBG-AE detection from influence caused by the static strain in a test specimen, the FBG sensor was installed by a remote adhesive configuration, i.e., one point of optical fiber was glued on the specimen, and the FBG sensor in the optical fiber was located away from the adhesive point. In the particular bonding way, the FBG sensor detected AE wave through an optical-fiber-based ultrasonic waveguide. In the first half of the paper, an ultrasonic experiment was conducted to show this installation technique can stably and accurately detect the behavior of Lamb wave modes in AE signals. With the help of the sensing characteristics, we clarified that a time difference between the arrival of S0 and A0 modes in a one AE signal had a linear relation to the distance between the AE source and the adhesion point when the length of optical fiber-based waveguide was fixed. Based on the examination, the linear AE source localization method was established using only one single FBG sensor. After confirming the ability of the proposed approach through a simulated AE experiment in a cross-ply CFRP laminate, we used the strategy to localize the actual damage-induced AE sources during a three-point bending test of the laminate.
  • Parameter sensitivity of CFRP retrofitted substandard joints by stochastic
           computational mechanics
    • Abstract: Publication date: 15 April 2020Source: Composite Structures, Volume 238Author(s): Özgür Yurdakul, Onur Tunaboyu, Ladislav Routil, Özgür AvşarAbstractThe response of both substandard as-built and CFRP retrofitted RC beam-column joints was investigated by a stochastic study to identify the effect of inherent uncertainties in material constitutive models. Since the scatter of the capacity is inevitably influenced by material properties, the relative impact of each material property on the global response was measured by the sensitivity analysis. It was conducted by evaluating the partial correlation coefficient between material properties and simulated response. First, experimentally validated deterministic nonlinear numerical models were developed in FE environment. After that, they were evolved to the stochastic level, which considers the randomness in prominent material parameters. The basic statistical characteristics and probability density functions of response variables were then provided by the probabilistic assessment. Finally, the most influential material parameters characterizing the quasi-static cyclic behavior of the as-built and retrofitted joints were outlined in accordance with the results of sensitivity analyses. In addition, the hysteric response of the as-built and retrofitted specimens was not only well-characterized by the numerical model but also local damages, such as large diagonal cracks in the as-built specimen and shear cracks after CFRP rupture in the retrofitted specimen, were adequately reproduced in the finite element environment.
  • Flexural behavior of concrete-filled SHS and RHS aluminum alloy tubes
           strengthened with CFRP
    • Abstract: Publication date: 15 April 2020Source: Composite Structures, Volume 238Author(s): Yao Zhu, Yu Chen, Kang He, Ran Feng, Xiaoyong Zhang, Qingxia Zhu, Chao TangAbstractConventional concrete-filled aluminum alloy tube (CFAT) can effectively delay the inward local buckling of aluminum alloy tube (AA). This paper experimentally and numerically investigates the suitability of strengthening square and rectangular hollow section (SHS and RHS) CFAT beams with a layer of carbon-fiber reinforcement polymer (CFRP) under four-point bending. Among 40 beams, 30 square and rectangular CFAT beams were strengthened with CFRP comprising three arrangement schemes of CFRP and 10 conventional square and rectangular CFAT beams were treated as reference beams. Flexural stiffness of square and rectangular CFAT beams are remarkably enhanced by external bonded CFRP, while the ductility is decreased. The bottom flange-bonded CFRP scheme is less effective in enhancing ultimate strength of CFAT beams than that of four sides-bonded CFRP scheme. New design approaches for evaluating both initial and post-yield flexural stiffness of square and rectangular CFAT beams strengthened with CFRP are proposed. FE models are correctly simulated to analyze the flexural behavior of square and rectangular CFAT beams strengthened with CFRP. CFRP strengthening technique using in this study can remarkably enhance the ultimate strength of square and rectangular CFAT beams and effectively delay the outward local buckling of AA tubes.
  • A broadband and tunable microwave absorption technology enabled by
           VGCFs/PDMS-EP shape memory composites
    • Abstract: Publication date: 15 April 2020Source: Composite Structures, Volume 238Author(s): Xiang Li, Yaofeng Zhu, Xuqing Liu, Ben Bin Xu, Qingqing NiAbstractA facile method for fabricating intelligent microwave absorber of vapor grown carbon fibers/Polydimethylsiloxane-epoxy resin shape memory composites (VGCFs/PDMS-SMEP) was proposed to deliver intelligently tunable and broadband microwave absorption performance. The maximal absorption intensity was regulated by varying the deformation of the composites driven by the superior shape memory property of SMEP, where practical the minimum reflection loss (RLmin) reaches −55.7 dB at 16.0 GHz with the thickness of 2.0 mm. The effective absorption bandwidth (EAB) reached 9.8 GHz, which covered the whole applied frequency range (8.2–18.0 GHz). The intelligent microwave absorption performance of the sample was attributed to robust conductive loss and dielectric loss enhanced by the dipole relaxations and multi-reflections. Thus, VGCFs/PDMS-SMEP composites serves as the key that really opens up opportunity for the application as flexible, shape memory and tunable high performance broadband microwave absorption absorber in frontiers such as wearable electronic devices, chips protection, stealth technology and information security.
  • Study on the mechanism of band gap and directional wave propagation of the
           auxetic chiral lattices
    • Abstract: Publication date: 15 April 2020Source: Composite Structures, Volume 238Author(s): Kai Zhang, Pengcheng Zhao, Cheng Zhao, Fang Hong, Zichen DengAbstractIn this study, the wave propagation properties in terms of the band gap and directions of wave propagation of the auxetic chiral structure are analyzed. The mechanism of generation of the band gap are carefully investigated. The auxetic chiral structure are assembled with the repeat unit cells and the unit cell contains a number of rigidly connected beams. The dynamic model of the unit cell are established by the principle of finite element method. The wave behaviors of the lattices are calculated by solving the dynamic model with the help of the Bloch’s theorem. The band structure are obtained and the effects of the chiral angles on the width and position of the band gap distributions are carefully studied. Especially, the mechanism of formation of the band gap are also analyzed by investigating the vibrational mode calculated by the commercial finite element software. The group velocities are calculated to analyze the effects of the geometrical parameters on the directional frequency-dependent energy flows in the structures. We also use the commercial finite element software to simulate the directional wave behaviors in the structure. We find that the first mode of the elastic wave spread only along certain specific directions in the auxetic chiral structure. The speed of wave propagation will be reduced, and the direction of wave propagation rotates counterclockwise when the chiral angle increases.
  • Nonlinear modeling of bamboo fiber reinforced composite materials
    • Abstract: Publication date: 15 April 2020Source: Composite Structures, Volume 238Author(s): Zhenyu Qiu, Hualin FanAbstractBamboo composites always exhibit nonlinear stress-strain behaviors in compression, shearing or even in tension. Piecewise functions have been applied to describe the nonlinearity of bamboo composites through pre-setting steps. The Ramberg-Osgood relation is a continuous and slide function and has been proved to be a better way to describe the nonlinear behaviors of materials. On the basis of fitting a large number of stress-strain curves of four types of bamboo composites, nonlinear Ramberg-Osgood model has been built for bamboo composites. Adjusting the control parameters, the Ramberg-Osgood relation can accurately model various types of stress-strain curves of the bamboo composites. To reflect the dispersion of the mechanical behaviors of the bamboo-based composites, a Ramberg-Osgood envelope method is proposed to comprise the variation of the nonlinear stress-strain curves. Nonlinear structural model for flexural bamboo beams is derived based on the Ramberg-Osgood equation. The structural model can consistently analyze the nonlinear flexural behavior of bamboo beams and predict the ultimate loads.
  • Influence of hygrothermal ageing on the mechanical properties of
           CFRP-concrete joints and of their components
    • Abstract: Publication date: 15 April 2020Source: Composite Structures, Volume 238Author(s): Karrar Al-Lami, Pierluigi Colombi, Tommaso D'AntinoAbstractExternally bonded (EB) fiber reinforced polymer (FRP) composites have been effectively employed to strengthen existing reinforced concrete (RC) structures. However, relatively limited information is available regarding the long-term behavior of FRP-concrete joints. In this paper, different experimental tests are employed to investigate the effect of hygrothermal ageing on the bond behavior of a carbon FRP composite applied to a concrete substrate and on the mechanical properties of the epoxy resin and FRP composite considered. The experimental campaign includes tensile tests of epoxy resin, carbon FRP (CFRP) coupon, pull-off tests of the CFRP bonded to the concrete substrate, and single-lap direct-shear tests of CFRP-concrete joints. Specimens were conditioned in warm water (38 ± 2 °C) for 500, 1000, and 1500 h to accelerate the possible degradation induced by a simulated high-moisture exposure environment. The parameters studied were the tensile properties of epoxy resin and CFRP coupons and the fracture energy of the CFRP-concrete interface, which was computed from the CFRP strain measured in the single-lap direct-shear tests using the digital image correlation (DIC) method. Results indicate that both the mechanical properties of the epoxy resin and the CFRP-concrete interface fracture energy were slightly affected by the exposure conditions.
  • Closed-form approximate solution for linear buckling of Mindlin plates
           with SRSR-boundary conditions
    • Abstract: Publication date: Available online 8 February 2020Source: Composite StructuresAuthor(s): M. Beerhorst, S. Thirusala Suresh BabuAbstractThe present work deals with the buckling analysis of rectangular Mindlin plates consisting of laminated composites with symmetrical, balanced lay-up or isotropic materials. Along the longitudinal edges the plate is rotationally restrained by springs. The transversal edges are simply supported. In agreement with common notation, the boundary conditions are abbreviated as follows: simply supported (S), rotationally restrained (R), and fully clamped (C). As loading situation axial compression is considered. Aiming at high computational efficiency the problem is solved by the Rayleigh-Ritz-method. Since well suited shape functions for deflection and rotations with very few variables are used, closed-form approximate solutions for the buckling load can be obtained. For verification exact transcendental solutions and/or high fidelity finite element analyses are employed. Additionally, results are compared to those of existing closed-form approximate solutions.Apart from the special case of simply supported longitudinal edges where all methods yield exact or nearly exact results, the present method shows clear advantages: 1. Due to the type of shape functions it is able deal with unsymmetrical boundary conditions. 2. For the case of both longitudinal edges fully clamped where all closed-form approximate solutions show the greatest deviations the present method is significantly more accurate.
  • An accurate higher order plate theory for vibrations of cross-laminated
           timber panels
    • Abstract: Publication date: Available online 8 February 2020Source: Composite StructuresAuthor(s): Thomas Furtmüller, Christoph AdamAbstractIn this contribution, bending vibrations of cross-laminated timber (CLT) panels are addressed. The focus is on the low to mid audio frequency range in view of the sound radiation properties of CLT. To this end, a plate theory recently proposed by the authors is adapted by introducing a deformation ansatz for the transverse displacement and neglecting insignificant terms, yielding a theory with six degrees of freedom. From the governing equations of motion, dispersion relations for the propagation of bending wave are derived, which also allow to compute the natural frequencies and mode shapes of bounded plates. The weak formulation of the equations of motion is presented. The accuracy of the proposed theory is validated for a simply supported rectangular CLT panel for which an analytical solution is available. The results are compared with first order shear deformation theory, revealing the limitations of this simplified theory in the present context. Finally, finite element solutions for the rectangular plate with non-classical boundary conditions are presented, as well as incorporating a floating floor construction, underlining the importance of numerical solutions for the practical application of this plate theory.
  • Anisotropic solid-like shells modeled with NURBS-based isogeometric
           approach: vibration, buckling, and divergence analyses
    • Abstract: Publication date: Available online 8 February 2020Source: Composite StructuresAuthor(s): Shirko Faroughi, Erfan Shafei, Timon RabczukAbstractWe proposed an IGA formulation for free vibration, buckling and divergence analyses of generally anisotropic solid-like composite shells. Recently developed Rayleigh–Ritz based methods are not accurate enough for curved shells since they are not able to capture twisting mode shapes. Here, we use the advantages of isogeometric analysis (IGA) and develop a three-dimensional higher-order continuous solid-like shell (SLS) model. Since the continuity of material orientation is crucial in numerical analysis of anisotropic shells, non-uniform rational B-splines (NURBS) are used to establish a smooth interpolation through the thickness and on the middle surface of the shell for both the geometry and displacement fields. The developed isogeometric SLS is coupled with Bézier extraction operators to represent continuity between multi-patch anisotropic domains. Numerical solutions for composite laminated shells with different boundary conditions are compared with analytical solutions or other solutions from the literature. In this context, we study the influence of span-to-thickness ratios, different shapes, modulus ratios, member aspect ratios and various layouts on the mechanical response. With the presented model, we were able to obtain the twisting mode shapes, which are not frequently observed in orthotropic and isotropic ones. We also study the influence of the polynomial order of the IGA formulation on the results.
  • Non-linear Bending Compliance of Thin Ply Composite Beams by Local
           Compression Flange Buckling
    • Abstract: Publication date: Available online 7 February 2020Source: Composite StructuresAuthor(s): F. Schadt, M. Rueppel, C. Brauner, Y. Courvoisier, K. Masania, C. DransfeldAbstractPassive spanwise bending shape-adaption has the potential to increase the efficiency and manoeuvrability of vehicles with wing-like structures. By utilisation of compression flange buckling, the in-plane stiffness can be tuned to design beams with contrasting pre-buckling and post-buckling bending stiffness. The investigated concept is experimentally validated using a thin-ply laminated composite four-point bending beam, which is designed to experience compression flange buckling in the span with constant moment. The bending stiffness was reduced by more than 41% after the onset of buckling which shows the effectiveness of compression flange buckling for non-linear bending compliance.
  • Simulation of edge impact and compression after edge impact in CFRP
    • Abstract: Publication date: Available online 7 February 2020Source: Composite StructuresAuthor(s): A. Arteiro, P.J. Gray, P.P. CamanhoAbstractThis paper presents the application of a composite damage model to predict the edge impact and compression after edge impact (CAEI) response of CFRP laminates. First, a mesh sensitivity analysis is performed showing that the mesh needs to be sufficiently fine to accurately capture the permanent out-of-plane deformation at the impact location, which acts as the initiation site that induces laminate compressive failure at early stages in the deformation process. The simulations of edge impact are correlated with the impactor load-displacement data, impact area, and visible crack length data available in the literature. The experimentally measured stress-displacement curves are used to validate the residual strength predictions. The shape and size of the damage inflicted by the edge impact events on different laminates is well predicted, as well as the residual strength of the laminates subjected to CAEI. The model proposed can accurately capture stacking sequence effects, predicting significant changes in the shape of the damaged area when only the stacking sequence changes, in agreement with the experimental observations.
  • Post-Impact Flexural Behavior of Carbon-Aramid/Epoxy Hybrid Composites
    • Abstract: Publication date: Available online 6 February 2020Source: Composite StructuresAuthor(s): A. Wagih, T.A. Sebaey, A. Yudhanto, G. LubineauAbstractHybrid polymeric composites are currently used in aerospace structures due to their specific strength and stiffness as well as larger design space. This paper presents an experimental study on residual flexural strength of impacted Carbon-aramid/Epoxy hybrid composite laminates. Specimens are designed in a sandwich form in which plies of aramid/epoxy represent the core and carbon/epoxy plies play the role of face sheets. This design is expected to take advantage of the high energy absorption capabilities of aramid/epoxy composites. We pre-damage such composites by performing low-velocity impact at different energy levels. Three-point bending tests then are used to measure the residual flexural strength for the impacted specimens. The damage sequence during three-point bending is monitored using a camera and, later on, with computed tomography. The results show that, unlike the all-carbon/epoxy laminates, the carbon fiber plies in the lower part of the laminate (non-impacted face) are not fractured after either the impact test or the three-point bending test. The damage is locally concentrated at the impacted face and the upper part of the aramid plies core. As a result, the strength losses are smaller, as compared to available results in the literature for carbon/epoxy composites, glass/epoxy and carbon fibers with aluminium core laminates.
  • Studies on the mechanical and absorption properties of achatina fulica
           snail and eggshells reinforced composite materials
    • Abstract: Publication date: Available online 5 February 2020Source: Composite StructuresAuthor(s): O.J. Gbadeyan, S. Adali, G. Bright, B. Sithole, A. OmojoolaAbstractThe present study focuses on the mechanical and absorption properties of composites reinforced by achatina fulica snail (S-shell) and eggshell particles (E-shell). Epoxy composites of snail and eggshell particles were prepared separately with the filler content ranging from 5 to 20% by weight. Hybrid composites of both fillers were also prepared and assessed. Specimens of the composites and hybrid composites with different percentage weights of the reinforcing materials were fabricated using the resin casting method. Mechanical properties such as tensile strength, Young’s modulus, impact strength, hardness and water absorption properties of the specimens were evaluated experimentally. It was observed that the addition of nano-size shell particles improves the mechanical properties of neat epoxy irrespective of the percentage weight of the reinforcement. The mechanical and water absorption properties of composites and hybrid composites varied depending on the amount of the reinforcement. Significantly, hybrid reinforcement by S-shell and E-shell particles offered superior properties in most cases. High percentage weight of calcium carbonate in these naturally sourced fillers and the synergistic effect of the S-shell and E-shells particle fillers can be attributed to high strength, stiffness, and decrease in water uptake of the composites.
  • Evaluation of infrared thermography methods for analysing the damage
           behaviour of adhesively bonded repair solutions
    • Abstract: Publication date: Available online 5 February 2020Source: Composite StructuresAuthor(s): U. Martens, K.-U. SchröderAbstractFor subsurface damage inspection of bonded repair patches, non-destructive inspection methods are needed. Additionally, monitoring the subsurface damage progress under loading is essential to gain knowledge for the repair design process. Infrared thermography is a temperature-based non-destructive inspection method. The method of optical lock-in thermography is commonly used for the steady-state detection of subsurface inhomogeneities while passive thermography can be used to monitor changes in surface temperature due to thermal energy dissipation. Here, the progress of subsurface damages is of interest. Both methods are analysed in terms of their applicability to monitor subsurface damage propagation under loading. This paper shows how these methods contribute to understand the degradation process of a mechanically loaded patch repair.
  • Effect Of Core Density On The Low-Velocity impact Response Of Foam-Based
           Sandwich Composites
    • Abstract: Publication date: Available online 5 February 2020Source: Composite StructuresAuthor(s): D. Feng, F. AymerichAbstractThe paper presents the results of an investigation into the effect of core density on the low-velocity impact response of foam-based sandwich composites. Drop-weight tests were conducted on sandwich panels with carbon/epoxy facesheets and a 10 mm thick PVC foam core. Three foam core densities (65, 100 and 160 kg/m3) and two facesheet layups ([0/903/0], [03/±45]S) were examined in the study. The analyses show that the influence of core density on the damage resistance of the panels is strongly correlated to the layup of the skin. While the damage developing in [0/903/0] panels is not affected by core density, the damage area in [03/±45]S panels reduces with increasing core density. The different influence of core properties on the damage response of [0/903/0] and [03/±45]S sandwich panels may be attributed to the different bending stiffness of the facesheets, with a response to impact dominated by global bending in panels with thin [0/903/0] skins as opposed to one mainly governed by local shear rigidity in panels with thicker [03/±45]S skins. FE analyses were finally carried out to assess the capability of a model developed by the authors to capture the role of foam density in the impact damage response of the panels.
  • Nonlinear Vibration Behavior of Functionally Graded Porous Cylindrical
    • Abstract: Publication date: Available online 5 February 2020Source: Composite StructuresAuthor(s): M.M. Keleshteri, J. JelovicaAbstractThe paper presents large amplitude free vibration response of functionally graded porous (FGP) cylindrical panels considering different shell theories and boundary conditions. Nonlinear governing equations are obtained based on two shell theories, first order shear deformation theory (FSDT) and higher order shear deformation theory (HSDT). The von Karman geometrical nonlinearity along with the Hamilton principle is utilized. Mechanical properties of the open-cell foam are assumed to vary continuously through the thickness. This graded porosity offers a smooth stress distribution along the thickness of the panel. Generalized differential quadrature method (GDQM) is utilized to discretize the nonlinear dynamic governing equations along with three different boundary conditions. To solve the set of equations that include highly nonlinear parameters, the harmonic balance method along with the direct iterative approach is used. The results present the influence of geometrical parameters, vibration amplitude, porosity distribution, shell theories and boundary conditions on the nonlinear frequencies. It is found that both porosity distribution and porosity coefficient have a remarkable effect on the nonlinear natural frequencies of FGP cylindrical panel. To enhance the dynamic response of the cylindrical panel, porosity should be avoided near the panels’ surfaces.
  • A Novel Three-Dimensional Structure Model of Biomimetic Staggered
    • Abstract: Publication date: Available online 5 February 2020Source: Composite StructuresAuthor(s): Rui Hao, DongXu Li, Wang LiuAbstractThe staggered structure is considered to be one of the key factors for the excellent mechanical properties of bone. In order to solve the problem of non-uniform stress distribution in the hard component of the original biomimetic staggered composites, a novel three-dimensional structure model with pores is proposed in this paper. By generalizing the shear lag theory model of the original staggered structure to the new model, the constitutive relation of the porous structure is established. On this basis, the stress distribution with respect to the aspect ratio of the hard prisms is studied. Finally, the two composite models are simulated by finite element method. The results show that stress in the novel structure tends to be uniformly distributed under external force. So it has higher stiffness and strength to mass ratio, and maintains stronger toughness. It is illustrated that pores in staggered structure can help to fully exploit the mechanical potential of each phase in the composites, providing an explanation for the existing of large number of voids in bone. This study may have an important inspiration for designing lightweight load-bearing composites with high efficiency of vibration isolation and cushioning.
  • Impact resistance of nacre-like composites diversely patterned by 3D
    • Abstract: Publication date: 15 April 2020Source: Composite Structures, Volume 238Author(s): Kwonhwan Ko, Suyeong Jin, Sang Eon Lee, Jung-Wuk HongAbstractMulti-layered composites structured by replicating biological creatures are very promising protective material applicable in various industries for the outstanding mechanical characteristics. Particularly, nacre is the most sought-after creature for biomimicry due to the exceptional impact resistance, secured by hierarchically patterned architecture. Therefore, numerous efforts have been devoted aiming to develop high functional composites by mimicking the nacre. However, optimization of dimensions and material properties for the nacre-like geometry has not been fully investigated thus far. In this study, we utilize a combination of fabrication, testing, and simulation to explore an optimal design of the nacre-like composite. Various types of 3D nacre-like architecture are designed, and corresponding specimens are fabricated using a dual-extruder 3D printer. Under drop weight impact loading, impact performances of each specimen are demonstrated. The test is simulated with finite element models of the nacre-like composite, and the experiment and numerical results are in good agreement. Both results reveal that the nacre-like composite outperforms the monolithic stiff material upon impact. Furthermore, adequate dimensions of each constituent and desirable material properties are determined. This insight on the nacre-like design can be employed as a guideline toward further optimization for a new generation of high-performance material systems.
  • Effect of extension-twisting and extension-bending coupling on a
           compressed plate with a cut-out
    • Abstract: Publication date: 15 April 2020Source: Composite Structures, Volume 238Author(s): Katarzyna Falkowicz, Hubert Debski, Pawel WysmulskiAbstractThis paper investigates the behaviour of thin-walled composite plates with a cut-out under compression. The effects of lamina ply orientation on the critical state and the behaviour of the plates in the post-critical range were examined. The scope of the research involved numerical modelling of linear and non-linear stability problems by the finite element method, using the simulation software ABAQUS®. The created numerical models were then verified experimentally. The study was performed on a plate with an unsymmetric stacking sequence of plies. To force buckling into a higher mode, an unsymmetric laminate with extension-twisting and extension-bending coupling was used. This approach led to obtaining the natural, lowest mode of buckling (flexural-torsional), one that ensures stable performance of the structure in the post-critical range (no transition to flexural mode).
  • Rapid prediction of cured shape types of composite laminates using a
           FEM-ANN method
    • Abstract: Publication date: 15 April 2020Source: Composite Structures, Volume 238Author(s): Ling Luo, Boming Zhang, Guowei Zhang, Yue XuAbstractThe specified cured shapes can be utilized in polymer-matrix composites design, though they might have assembling difficulties or residual stresses. This study develops an integrated methodology to rapidly predict the cured shapes of carbon/epoxy composite laminates under different ply-stacking sequences based on the thermo mechanical finite element method (FEM) and artificial neural networks (ANNs). About 64 million networks were trained and validated to determine the best ANN models, which could approximate the complex nonlinear relationships between lay-up sequences and cured shape types. Six T800/epoxy specimens with different lay-up sequences were manufactured by an autoclave process to verify the FEM and the ANN. The correctness of the FEM model was verified by experiments. Experimental results also demonstrated that four ANN models (network structures: (250, 250, 100), (500, 250, 250, 100), (500, 250, 250, 100, 100), and (500, 100, 250, 250, 100, 100)) performed well with high generalization performance for the cured shape types’ prediction.
  • Stability analysis of laminate profiles under eccentric load
    • Abstract: Publication date: 15 April 2020Source: Composite Structures, Volume 238Author(s): Pawel Wysmulski, Hubert Debski, Katarzyna FalkowiczAbstractThe study investigates short thin-walled channel section columns made of a carbon-epoxy laminate. The tested columns were subjected to compression, including an eccentric compressive load relative to the gravity center of the cross section of the column. The boundary conditions applied in the study reflected simple support of the column. The scope of the study involved determining the effect of eccentric load on the structure’s stability and load-carrying capacity. At the same time, a numerical analysis by the finite element method was performed using the commercial simulation software Abaqus®. The non-linear numerical analysis of the compressed profiles was performed by the Newton-Raphson method. Failure of the composite material was described using a progressive damage model, wherein damage initiation in the composite material was described based on Hashin’s failure criteria while the evolution of damage was described by the energy-based progressive damage criterion. Results predicted by the numerical model were validated by experimental tests performed on real structures. The results enabled a comprehensive description of the composite material’s failure, starting from failure initiation until the total loss of load-carrying capacity of the column.
  • Microwave absorbing structure using periodic pattern coated fabric
    • Abstract: Publication date: 15 April 2020Source: Composite Structures, Volume 238Author(s): Won-Ho Choi, Byeong-Su Kwak, Jin-Hwe Kweon, Young-Woo NamAbstractIn this study, a microwave absorbing structure consisting of a periodic pattern coated glass fabric (PPCF) and a glass-fiber/epoxy composite as the spacer is presented using a practical approach for application in aircraft. To fabricate a PPCF, a carbon-based conducting material bar coating device was used. To test the performance of the PPCF, an X-band (8.2–12.4 GHz) microwave absorbing structure was fabricated using an autoclave and measured using a free-space measurement system. The return loss of the fabricated PPCF microwave absorbing structure was −27 dB at the resonance frequency, and the measurement result was well matched with the simulation result. Since the pattern was implemented on an uneven surface, the performance stability of the distribution of sheet resistance on the surface, pattern spreading phenomena, and waviness of patterns was verified using a simulation method. The simulation result showed good performance stability. To verify the mechanical properties, an interlaminar shear strength (ILSS) test was performed. Since the pattern on the glass fabric can act in a similar way to a defect, there is a high probability of mechanical property degradation. However, the ILSS test results of the PPCF specimen was comparable with a pure glass-fiber/epoxy composite.
  • Full-range behavior of fiber reinforced cementitious matrix
           (FRCM)-concrete joints using a trilinear bond-slip relationship
    • Abstract: Publication date: Available online 4 February 2020Source: Composite StructuresAuthor(s): Xingxing Zou, Lesley H. Sneed, Tommaso D'AntinoAbstractInterfacial debonding of fiber reinforced cementitious matrix (FRCM)-concrete joints can be considered as a mainly mode-II fracture process, a problem that can be solved by accounting for one-dimensional interfacial shear stress-slip relationships. This paper presents an analytical approach to predict the load response of FRCM-concrete joints by adopting a trilinear bond-slip relationship consisting of a linear-elastic branch, a softening branch, and a friction branch. The applied load-global slip response of FRCM-concrete joints with (relatively) long bonded length includes five stages: elastic, elastic-softening, elastic-softening-debonding, softening-debonding, and debonding stages. Closed-form solutions of the interfacial slip, shear stress, and axial stress (or strain) distribution along the bonded length are provided. The response of FRCM-concrete joints with (relatively) short bonded length is examined. The effective bond length and a critical length for the existence of the snap-back phenomenon are derived. Experimental results reported in the literature are used to calibrate the parameters needed for the analytical approach. The analytical results are then compared with experimental results and with numerical results determined using a finite difference method (FDM). Finally, the capability of determining the parameters in the trilinear bond-slip relationship using a neural network (NN) with the experimental load response as the input is investigated.
  • Modeling and design of a class of hybrid bistable symmetric laminates with
           cantilever boundary configuration
    • Abstract: Publication date: Available online 4 February 2020Source: Composite StructuresAuthor(s): Aghna Mukherjee, Michael Ian Friswell, Shaikh Faruque Ali, A. ArockiarajanAbstractMultistable laminates have been widely analyzed in the recent past for their potential in morphing applications. However, all the analytical models developed up until now have taken into account only the free-free boundary condition. In this work two objectives are met: (a) an analytical model is developed, which extends the previously available models in literature to account for the cantilever boundary condition for a special class of hybrid bistable symmetric laminates (HBSL); (b) the previously proposed HBSL is modified by replacing the aluminum layers with bi-direction glass-epoxy prepregs in the layup. It is observed that the modified layup has a curvature similar to the previously proposed HBSL while maintaining bistability. The analytical model developed here successfully captures the equilibrium shapes and the snap-through behavior for this special class of laminates which is validated against the results obtained using ABAQUS® and experiments. The developed model is then subsequently used to study the design space and bistability characteristics of the HBSL and the proposed modified layup (m-HBSL) in the cantilever boundary condition.
  • Chemical prestressing of high-performance concrete reinforced with CFRP
    • Abstract: Publication date: Available online 4 February 2020Source: Composite StructuresAuthor(s): Mateusz Wyrzykowski, Giovanni Terrasi, Pietro LuraAbstractChemical prestress (self-prestress) is a process, in which expansion of concrete with special additives can be used to generate tension in the reinforcement and prestress in the concrete. Until now, the prestress levels that could be reached with this technique were usually lower than with traditional (external) prestressing. With the new family of expansive high-performance concretes (HPC) developed by us, very high levels of residual expansion can be achieved without compromising the durability and still reaching very good mechanical properties of the concrete. In this paper, we combine the expansive HPC with tendons made of ultra-high modulus (>400 GPa) carbon fiber reinforced polymers (CFRP). Through the expansion of the concrete and its bond with the sand-coated tendons, we could introduce tensile stresses of more than 600 MPa in the tendons (for 1% reinforcement ratio), corresponding to more than 4 MPa compressive stress (prestress) in the concrete. 4-point bending tests show that the chemical prestress increased the cracking moment of slender concrete beams more than three times compared to the reference concrete. Our long-term tests of the strains of the tendons show that the losses of prestress due to shrinkage and compressive creep are very low.
  • On the energy release rate extraction and mixed mode behavior of fatigue
           cohesive model
    • Abstract: Publication date: Available online 4 February 2020Source: Composite StructuresAuthor(s): Tao Chongcong, Zhang Chao, Ji Hongli, Wu Yipeng, Qiu JinhaoAbstractThis paper presents a comprehensive study on the energy release rate (ERR) extractions and mixed mode behavior of fatigue cohesive model. The development of the non-linear cohesive zone ahead of a crack tip is influenced by multiple factors, where the extractions of ERRs and mode ratios are crucial for accurate fatigue analysis in Paris law-based models. Investigations into the effects of different parameters e.g. interfacial strengths, shapes of the cohesive laws and element sizes on the extracted ERRs are studied. In addition, two novel mixed mode bending models i.e. multi-stage mode ratio (MSMR) and continuously various mode ratio (CVMR) models are proposed for mixed-mode behavior study. All results are compared to the theoretical fracture mechanics analysis and to each other. It is found that if the interfacial strength becomes too low, an excessively long cohesive zone can form, where the mode ratio could significantly deviate from the true value and negatively impact the accuracy. The shape of cohesive laws is also found to influence the ERRs and mode ratios to some extent but are not the dominating factor.
  • The quasi-static axial compressive properties and energy absorption
           behavior of ex-situ ordered aluminum cellular structure filled tubes
    • Abstract: Publication date: Available online 4 February 2020Source: Composite StructuresAuthor(s): Han Wang, Mingming Su, Hai HaoAbstractIn this study, the ex-situ ordered aluminum cellular structure filled tubes with different filler types, filling ratios and filling positions were fabricated by inserting the ordered aluminum cellular structure fillers into the aluminum tubes directly. The ordered aluminum cellular structure fillers were prepared by the selective laser sintering and the infiltration casting. The compressive properties and energy absorption behavior of ex-situ ordered aluminum cellular structure filled tubes were assessed by quasi-static axial compression tests. The effects of the ordered cellular structure types, filling ratios and filling positions on compressive properties and energy absorption behavior of ex-situ ordered aluminum cellular structure filled tubes were investigated. The results show that both the uniform and graded ordered aluminum cellular structures as filler materials can significantly improve the compressive properties and energy absorption behavior. Meanwhile, the compressive properties and energy absorption behavior of ex-situ ordered aluminum cellular structure filled tubes can be tailored by changing the filling ratios and positions. It is noticed that the ex-situ ordered aluminum cellular structure vertically filled the middle part of the thin-walled tubes exhibit superior compressive properties and energy absorption behavior compared with the ex-situ ordered aluminum cellular structure horizontally filled the bottom of the thin-walled tubes.
  • The compressive response of octet lattice structures with carbon fiber
           composite hollow struts
    • Abstract: Publication date: Available online 4 February 2020Source: Composite StructuresAuthor(s): Xiao Liu, Vahidreza Alizadeh, Christopher J. HansenAbstractOctet lattice structures were designed with carbon fiber reinforced polymer (CFRP) composite hollow cylindrical struts to improve the specific compressive strength and stiffness of these lightweight structures. A joint connector was designed and manufactured from balanced [0/90] CFRP laminates to assemble the designed octet lattice structures. The compressive modulus and strength of CFRP hollow strut-based lattice structures were measured under quasi-static compression. Two competing failure mechanisms were observed. The fiber fracture of hollow struts dominated the failure of lattice structures with a relative density (ρ-) of 2.17%. In contrast, lattice structures with lower relative densities (ρ-= 1.33% and 0.85%) failed by Euler buckling of the hollow struts. To gain further insight of the compressive behavior of the lattice structures, an analytical model and a series of finite element (FE) models were developed. The predictions showed good agreement with experimental observations of both the compressive properties and failure behaviors. The results demonstrate that CFRP hollow tube-based octet lattice structures exhibited significantly higher relative strength and stiffness than CFRP solid strut-based counterparts. These superior properties of CFRP hollow strut-based octet lattice structure show a strong potential in high performance lightweight load-bearing application.
  • Analytical buckling solution of magneto-electro-thermo-elastic cylindrical
           shells under multi-physics fields
    • Abstract: Publication date: Available online 4 February 2020Source: Composite StructuresAuthor(s): Yiwen Ni, Shengbo Zhu, Jiabin Sun, Zhenzhen Tong, Zhenhuan Zhou, Xinsheng XuAbstractA new analytical buckling solution of a cylindrical shell made of two-phase magneto-electro-thermo-elastic (METE) composites under multi-physical fields is obtained by a Hamiltonian-based approach. Two types of technologically important distribution model are considered: continuous fibers and laminates. Based on the Reissner’s shell theory, the exact solution expanded into symplectic series is rigorously obtained from governing equations under the Hamiltonian description which has four possible forms of explicit expressions. Accurate critical buckling loads and analytical buckling mode shapes for various boundary conditions are obtained. A comprehensive comparison is presented to verify the proposed solution and very good agreement is reported. Effects of geometrical parameters, boundary conditions, cases of eigenfunctions, volume fractions and external magneto-electro-thermal loadings on buckling behaviors of the shell are investigated also.
  • Design-oriented approach to determine FRC constitutive law parameters
           considering the size effect
    • Abstract: Publication date: Available online 4 February 2020Source: Composite StructuresAuthor(s): Eduardo Galeote, Ana Blanco, Albert de la FuenteAbstractTensile strength constitutive laws for fibre reinforced concrete (FRC) are commonly defined through the parameters of flexural tests conducted on standard prismatic specimens. However, there are no specific criteria to determine such parameters using small specimens that could simplify the testing procedure and provide more representative results of slender structural FRC elements. In this line, the influence of size effect becomes an issue particularly relevant during the characterisation stage given that the residual strength decreases while increasing the size of the element. The objective of this document is to propose a methodology to obtain the parameters of the constitutive law using small specimens. For this, FRC residual strength was determined through three-point bending tests on prismatic notched beams of 40x40x160, 100x100x400 and 150x150x600 mm. An analytical model based on sectional analyses aimed at reproducing the flexural strength of FRC was used to assess the results of the alternative methodology to determine the parameters for the constitutive law. The results show that an approach based on the rotation instead of the crack opening as the reference parameter to estimate the stresses for the constitutive law leads to results less influenced by the size effect when designing small elements.
  • Computational optimization for porosity-dependent isogeometric analysis of
           functionally graded sandwich nanoplates
    • Abstract: Publication date: Available online 3 February 2020Source: Composite StructuresAuthor(s): P. Phung-Van, A.J.M. Ferreira, Chien H. ThaiAbstractA simply and effectively computational optimization for porosity-dependent isogeometric analysis of functionally graded (FG) sandwich nanoplates is proposed for the first time. Porosity-dependent material properties are defined via the modified power law function. The distribution of ceramic volume fraction is approximated by using the multi-patch B-spline basis functions through the thickness direction. This approach ensures smoothly and continuously vary material properties across each layer, and automatically satisfies the C0-continuity at each layer interfaces. To consider length scale effects, the Eringen’s nonlocal elasticity theory is used to model porous FG sandwich nanoplates. Based on a combination of NURBS formulations and four variables refined plate theory, governing equations of the nanoplates are derived and employed to obtain natural frequencies of the porous FG sandwich nanoplates. The present approximation is easy to satisfy the requirement of at least third order derivatives of basis functions in approximate formulations of nanoplates. To save computational costs, an adaptive hybrid evolutionary firefly algorithm is used. Continuous design variables including the thickness of each layer and the ceramic volume fraction at control points are considered for constraint optimization problems. New results are performed and considered as benchmark results for further studies on the porous FG sandwich nanoplates.
  • Ultrasonic Guided Wave Scattering due to Delamination in Curved Composite
    • Abstract: Publication date: Available online 3 February 2020Source: Composite StructuresAuthor(s): Rajendra Kumar Munian, D Roy Mahapatra, S GopalakrishnanAbstractWave propagation in a curved composite structure having delamination is simulated using time domain spectral finite element (TSFE) method that enables fast computation with higher-order field interpolation. Curved structures are very common in aerospace, marine and other composite structural components and understanding ways to detect delamination in these curved structures with the help of ultrasonic guided wave simulation is essential. Guided wave interaction with curved region progressively causes mode converted waves, which are present in both reflected as well as transmitted wave packets. The details are poorly understood. The additional wave packets due to interaction cause difficulty in identification of damaged induced responses. Mode conversion and reflection from the curved section reduce the useful signal strength to interrogate any delamination in the curved region. Guided wave interaction with the curved section in an L-shaped structure and a structure with T-joint are studied using TSFE simulation. Simulation results are validated using analytical solutions. Mode conversion and transmission in T-joint is studied using numerical simulation with experimental validation. Signal loss due to mode conversion and reflections at different frequencies is investigated in terms of geometric and wave parameters, which promises to identify the appropriate frequencies and choice of wave mode for monitoring.
  • Response of foam concrete-filled aluminum honeycombs subject to
           quasi-static and dynamic compression
    • Abstract: Publication date: Available online 3 February 2020Source: Composite StructuresAuthor(s): Hongyuan Zhou, Xuejian Zhang, Xiaojuan Wang, Yonghui Wang, Tianfei ZhaoAbstractTo prevent premature failure, aluminum honeycombs of the same areal density with and without foam concrete filling subjected to quasi-static and dynamic compression are experimentally tested. The influence of major governing factors including cell size of honeycomb, density of foam concrete, and loading rate on the performance in terms of compressive strength and energy absorption capacity are systematically examined. It is found that without foam concrete filling, the out-of-plane strength and energy absorption capacity of honeycomb of the same areal density increase with decreasing cell size, under both quasi-static and dynamic crushing. With foam concrete filler, the load bearing and energy absorption capacity of the honeycombs increase by 33%-207% compared to those of the corresponding foam concrete and honeycomb added up separately, and increase with increasing foam concrete density and decreasing honeycomb cell size, regardless of being compressed quasi-statically or dynamically.
  • The effect of tab orientation on the toughening mechanisms produced by
           interlocked interlaminar thin-ply CFRP reinforcements
    • Abstract: Publication date: 15 April 2020Source: Composite Structures, Volume 238Author(s): J.A. Pascoe, S. Pimenta, S.T. PinhoAbstractThe use of interlaminar reinforcement units, containing an interlocked tab-and-slit geometry, is a new concept for improving interlaminar fracture toughness. It was recently shown that such reinforcement units are capable of substantially increasing mode I fracture toughness, but mode II fracture toughness was unaffected.This paper presents an investigation into the effect of tab orientation on the toughening mechanisms, comparing the experimentally determined Mode I and II interlaminar fracture toughness for different tab orientations.The results show that the previously reported lack of mode II toughness increase was due to an unsuitable tab orientation. With a better choice of tab orientation a mode II propagation toughness increase (of 23.5%) could be obtained, while simultaneously increasing the mode I propagation toughness further than previously reported (up to a 109% improvement).Fractography was used to investigate the toughening mechanisms. It was found that the two main toughening mechanisms are crack bridging (in mode I) and deflection of the delamination path (in both mode I and II). The relationship between the tab orientation and the obtained increase of fracture toughness can be explained by the effect of tab orientation on these mechanisms.
  • Damage resistance and low-velocity impact behaviour of hybrid composite
           laminates with multiple thin steel and elastomer layers
    • Abstract: Publication date: 15 April 2020Source: Composite Structures, Volume 238Author(s): Denise Düring, E. Petersen, D. Stefaniak, C. HühneAbstractIn the presented investigation composites consisting of carbon and glass fiber reinforced plastics in combination with steel and elastomer layers are subjected to experimental drop-weight impact tests and compression after impact tests. The objective is to study the low-velocity impact behaviour, damage resistance and residual strength of composite laminates dependent on position and proportion of additional layers. In continuation of earlier studies two additional laminate configurations containing thin steel layers and two elastomer layers are tested. Impact damage and damage tolerance are determined respecting the aspect of differing bending stiffnesses and structure densities. It is found that concerning the elastomer addition the damage area, which mainly depends on the elastomer layer position, is an essential influencing factor on the residual strength. The steel addition leads to wide delaminations but high residual strengths.
  • Tensile properties of GFRP laminates after exposure to elevated
           temperatures: Effect of fiber configuration, sample thickness, and time of
    • Abstract: Publication date: 15 April 2020Source: Composite Structures, Volume 238Author(s): Hamed Ashrafi, Milad Bazli, Armin Jafari, Togay OzbakkalogluAbstractThis study investigates the tensile properties of various GFRP laminates after exposure to elevated temperatures. Fiber configuration, exposure temperature and laminate thickness were considered as the test variables. A total number of 180 specimens were tested in tension to obtain the mechanical properties of GFRP laminates. Alongside the mechanical tests, SEM analyses were conducted on selected samples before testing to investigate the resin, fiber, and their interface damages. Regardless of the sample type, it was generally observed that the reduction rate in the tensile strength increased with an increase in the exposure time and a decrease in the laminates’ thickness. The results of tensile tests after exposure to elevated temperatures showed that the laminates with continuous unidirectional fibers performed the best, laminates with chopped strand randomly distributed fibers performed the worst, and the performance of the laminates with woven continuous fibers was somewhere in between. The maximum tensile strength reductions for the unidirectional and woven laminates were about 50% after exposure to 300 °C, whereas random chopped strand laminates lost almost all of their load carrying capacity under this exposure condition.
  • Optimal design method for composite blades using stiffness weights
    • Abstract: Publication date: 15 April 2020Source: Composite Structures, Volume 238Author(s): Long Zhang, Purong Jia, Tao Huang, Bo WangAbstractBend–twist coupling effect of composite materials can be used to reduce blade torsion deformation and improve blade efficiency. In this study, stiffness weight coefficients and load coefficients were introduced to quantify the ply sequence and bend–twist load condition. Composite stator blades were simplified into symmetric unbalanced cantilever laminated to verify the stiffness weight coefficients and load coefficients. Moreover, the bend-twist coupling effect of the symmetric laminates with different ply angles and stiffness weight coefficients under various load coefficients was investigated through experiments, classical laminate theory, and finite element analysis. An optimization method using stiffness weight coefficients was proposed. The optimal goal is to minimize blade torsion and curvature to improve blade efficiency. And the global optimal solution using traversal search method was obtained to compare with the optimal solution in this method. A 40-ply blade was optimized using this method. The optimal results indicate that this method can reduce the calculation amount for the optimization by eliminating the ply combination which does not meet optimization goals, and the errors between optimal solution of this method and global optimal solution are acceptable. This optimization method can serve as a reference and basis for the optimal design of composite blades.
  • Failure analysis of single lap composite laminate bolted joints:
           Comparison of experimental and numerical tests
    • Abstract: Publication date: 15 April 2020Source: Composite Structures, Volume 238Author(s): Benoit Montagne, Frédéric Lachaud, Eric Paroissien, Dominique Martini, Fabrice CongourdeauAbstractCarbon fiber reinforced plastics (CFRP) are widely used in aircraft industry because of their high mechanical properties. However these properties considerably drop when composite materials are drilled and bolted. Thus, it is important to master the composite bolted joint behavior to avoid a structural failure. Experimental test on single lap bolted joints with various end distance have been led. The failed specimens are analysed thanks to XR computed tomography (XR-CT) and digital image correlation (DIC). The results are compared with a three dimensional finite element model involving a progressive damage model for the composite material. It is based on a progressive damage model of the composite material. The global behavior and the damages computed are in good agreement with the experimental results. But, contrary to the experimental observations, the computed damage scenarios are the same for all the tested end distance.
  • Shear response of ultra-lightweight CFRP cores
    • Abstract: Publication date: 15 April 2020Source: Composite Structures, Volume 238Author(s): Pablo Vitale, Gaston Francucci, Helmut Rapp, Ariel StocchiAbstractIn this work the shear performance of ultra-lightweight (ULW) carbon fiber reinforced polymer (CFRP) cores with 3-dimensional (3D) geometries is analyzed. The cores are made from a machined CFRP laminate. Using the interlocking method, CFRP sheets are assembled in order to obtain a square pattern. The density of all manufactured cores is achieved below than 48 kgm−3. Through simple analytical mechanical models, it is possible to predict the failure behavior of the panels. Finite element analyses (FEA) are carried in order to contrast and validate the theoretical models. Good agreement among theoretical, finite element and experimental results is found. The experimental results show that the controlling failure mechanisms are shear failure of the base material or debonding, also predicted successfully by the numerical and analytical approaches. Finally, the cores are compared favorably as well with other competing known materials.
  • Thermal buckling of curvilinearly stiffened laminated composite plates
           with cutouts using isogeometric analysis
    • Abstract: Publication date: 15 April 2020Source: Composite Structures, Volume 238Author(s): Balakrishnan Devarajan, Rakesh K. KapaniaAbstractThis research presents the Non-Uniform Rational B-Splines (NURBS) based isogeometric finite element analysis of stiffened laminated composite plates. A first-order shear deformation theory is used to derive the governing equations by employing a variational formulation. Isotropic, orthotropic and laminated composite plates stiffened with multiple curvilinear stiffeners of different profiles are investigated. A novel way to achieve displacement compatibility between the panel and stiffeners interfaces is introduced. An easy way of modeling plates with complicated cutouts by using edge curves and generating a ruled NURBS surface between them is described. Influence on the critical thermal buckling load due to the presence of circular and elliptical cutouts is also investigated. Results of parametric studies are presented which show the influence of ply orientation, size and orientation of the cutout, and the position and profile of the curvilinear stiffener. The numerical examples show high reliability and efficiency of the proposed formulation when compared to other published solutions and those obtained using ABAQUS, a commercial software.
  • A continuation-based method for finding laminated composite stacking
    • Abstract: Publication date: 15 April 2020Source: Composite Structures, Volume 238Author(s): A.D. ViqueratAbstractA method of recovering laminate ply stacking sequences from a set of up to twelve lamination parameters using polynomial homotopy continuation techniques is presented. The ply angles are treated as continuous variables, and are allowed to take any value between -90° and +90°. The individual plies are assumed to be orthotropic and have constant stiffness. The method is fully deterministic, and does not rely on an optimisation process to establish the stacking sequence. Polyhedral continuation methods are used to limit the solution space in which the stacking sequences are sought. The method can reliably find every stacking sequence solution that exists to achieve a precisely specified set of lamination parameter “targets”, with the number of real solutions to a feasible combination of target properties found to vary from 1 to over 100. The same method is also demonstrated to be able to find stacking sequences to satisfy a set of specified ABD stiffness matrix terms, as might be required following a direct-stiffness modelling design process.
  • Twisted composite structures made by 4D printing method
    • Abstract: Publication date: 15 April 2020Source: Composite Structures, Volume 238Author(s): Suong V. Hoa, Xiao CaiAbstractThis paper presents the determination of the configurations of twisted laminates made by 4D printing of composites (4DPC) method. Flat stacks of composite prepregs are laid onto a flat mold. Upon curing and cooling to room temperature, the flat stack becomes curved and twisted. The configurations of the twisted laminate are determined using both calculated method (FEM) and experimental measurement. Reasonable agreement is obtained.
  • Residual Impact Strength of Glass/epoxy Composite Laminates after Solid
           Particle Erosion
    • Abstract: Publication date: Available online 1 February 2020Source: Composite StructuresAuthor(s): A.M. Amaro, A.J.R. Loureiro, M.A. Neto, P.N.B. ReisAbstractThe main goal of this work is to study the effect of solid particle erosion on the impact fatigue life. For this purpose, impingement angles of 10°, 45° and 90°, stand-off distances of 75 mm, 100 mm and 125 mm and particles size of 20 mesh, 24 mesh and 54 mesh were considered. After exposure to corundum particles flow, during 20 seg and constant pressure of 2 bar, the glass/epoxy laminates were evaluated in terms of weight loss and depth of eroded area. Finally, all samples were submitted to multi-impacts until full perforation. From the experimental tests, it can be concluded that weight loss and depth of eroded area increase with the increasing of impingement angle, reaching maximum values for 90°. In terms of distance between nozzle and target, higher values promote larger and shallower damaged areas, while smaller particles are responsible by lower weight loss and depth. Finally, the fatigue life is very sensitive to the erodent size, but the opposite tendency occurs for impingement angle and stand-off distance, alternating according to their values.
  • Serviceability and ultimate behaviour of GFRP reinforced lightweight
           concrete slabs: experimental test versus code prediction
    • Abstract: Publication date: Available online 1 February 2020Source: Composite StructuresAuthor(s): Agnieszka Wiater, Tomasz SiwowskiAbstractThe advantages of GFRP reinforcement and lightweight concrete (LWC) in relation to bridge deck slabs encourage the extension of knowledge regarding the possibilities of combining these two materials and to use the synergy of benefits that can be achieved in the construction and/or rehabilitation of bridges. This paper presents the research aimed to evaluate the static performance of LWC slabs reinforced with GFRP bars for flexure without shear reinforcement. The serviceability and ultimate behaviour were evaluated for the LWC/GFRP slabs in comparison with those made of normal-weight concrete (NWC). Comparison of measured and ACI code predicted behaviour of LWC and NWC slabs is also presented. Generally, the serviceability and ultimate behaviour of LWC slabs under static load was less favourable than their NWC counterparts. Research revealed the considerable differences between the NWC and LWC slabs behaviour as well as between test results and ACI code predictions.
  • Low velocity impact behavior of carbon fibre composite curved corrugated
           sandwich shells
    • Abstract: Publication date: Available online 1 February 2020Source: Composite StructuresAuthor(s): Jin-Shui Yang, Wei-Ming Zhang, Fang Yang, Si-Yuan Chen, Rüdiger Schmidt, Kai-Uwe Schröder, Li Ma, Lin-Zhi WuAbstractComposite thin-walled curved structures are widely used in aerospace, marine, automotive and building engineering application. In this paper we design and fabricate a series of carbon fibre composite axial and circular corrugated sandwich cylindrical panels (ACSCPs and CCSCPs) by an in-house hot press moulding method. Low velocity impact tests are carried out to evaluate the impact resistance and failure mechanisms of such structures. Furthermore, validated finite element analysis (FEA) models based on the Hashin failure criteria are adopted to study the effects of the relative density, impact energy and impact position on their impact responses. It is observed that generally the peak forces and absorbed energies of the specimens ascend with the increase of the relative density. The impact responses, especially the ultimate loads of the present structures are particularly dependent on the impact position, but insensitive to the increase of the impact energy. By comparison, the ACSCPs generally have a more excellent impact resistance and energy absorption properties than that of CCSCPs. In addition, the corresponding energy contribution of the components for the ACSCPs and CCSCPs under different impact energy is also revealed, which could be useful for the multifunctional design of such kinds of composite curved sandwich structures.
  • Strengthening bonding strength in NiTi SMA fiber-reinforced polymer
           composites through acid immersion and Nanosilica coating
    • Abstract: Publication date: Available online 1 February 2020Source: Composite StructuresAuthor(s): Yongchao Zhang, Changwen MiAbstractExtensive applications of shape-memory alloy fiber-reinforced polymer composites are limited by the weak bonding conditions between alloy fibers and their surrounding matrix. In this work, we aim to investigate an effective means for elevating the interfacial bonding between nickel-titanium shape-memory alloy fibers and epoxy matrix by the combination of nitric acid immersion and nanosilica particles coating. Three experimental tests were carefully designed and conducted for verifying and validating the proposal. They include the uniaxial tensile test of chemically etched fibers, the pull-out test against a single fiber embedded inside a cylindrical epoxy matrix, and the three-point flexural test on fiber-reinforced polymer composites. Extensive parametric tests were performed in order to both qualify and quantify the effects of chemical etching, nanoparticle coating, and their combination. Experimental tests were followed a comprehensive analysis on both the mechanical behavior and the microscopic and macroscopic morphology of the specimens. Experimental results suggest the possibility of effectively elevating the interfacial bonding strength between nickel-titanium shape-memory alloy and epoxy matrix by the appropriate coupling of acid immersion and nanoparticle coating. Microscopical optimization mechanisms were also proposed and validated in terms of both intergranular and transgranular cracking along fiber/matrix interface subjected to shear loading.
  • Experimental and numerical investigations on concrete filled carbon FRP
           tube (CFRP-CFFT) columns manufactured with ultra-high-performance fibre
           reinforced concrete
    • Abstract: Publication date: Available online 1 February 2020Source: Composite StructuresAuthor(s): C. Fang, M.S. Mohamed Ali, A.H. SheikhAbstractThis study aims to investigate the structural responses of five concrete filled carbon FRP tube (CFRP-CFFT) columns manufactured with ultra-high-performance fibre reinforced concrete (UHPFRC) under concentric or eccentric loading protocols with eccentricities ranging from 0.067D (depth) to 0.57D (depth). One CFRP-CFFT UHPFRC beam with the same cross-section configuration used for columns was subjected to four-point flexural bending. Furthermore, finite element (FE) analysis incorporating concrete damage plasticity (CDP) model was also conducted to simulate the behaviours of CFRP-CFFT UHPFRC members; the corresponding load-axial displacement and load-lateral deflection relationships were numerically generated to compare with the experimental results. FE simulations exhibit a high correlation compared to experimental results, which further highlights the applicability of FE modelling in predicting the structural response of the CFRP-CFTT UHPFRC members. A load-moment (P-M) interaction envelope was generated from the FE modelling to facilitate the development of a design guideline of CFRP-CFFT UHPFRC columns subjected to axial load with a varying eccentricity.
  • Study on Bearing Strength and Failure Mode of a Carbon-Epoxy Composite
           Laminate for Designing Bolted Joint Structures
    • Abstract: Publication date: Available online 1 February 2020Source: Composite StructuresAuthor(s): Donghyun Yoon, Sangdeok Kim, Jaehoon Kim, Youngdae DohAbstractA composite single-lap bolted joint was experimentally studied and its bearing behavior was predicted numerically. Prior to performing the experiment, an appropriate e/D ratio of the composite material was determined via double-lap bolted joint tests. Using the obtained e/D ratio, specimens were manufactured, and single-lap composite bolted joint tests were subsequently performed. Various joint tests were conducted with the number of bolt holes, pre-torque, and thickness as experimental variables. The preferred bearing failure mode was observed with the designed e/D ratio and bearing strength increased with increasing tightening torque. The bearing strength was significantly affected by the projected bearing area and exhibited a linearly proportional relation with the joint bearing area. The fracture mechanism was observed using optical microscopy, indicating fiber buckling, breakage, and delamination induced from the initial damage. An energy-based progressive failure analysis (PFA) was implemented to predict the composite bolted joints strengths. The adopted PFA accurately predicted the strength of the bolted joint in range of 12%.
  • Microstructural and mechanical assessment of the causes of failure of
           floors made of polyurethane-cement composites
    • Abstract: Publication date: Available online 31 January 2020Source: Composite StructuresAuthor(s): Łukasz Sadowski, Jerzy Hoła, Andrzej Żak, Agnieszka ChowaniecThe article presents the results of microstructural and mechanical testing of a floor made of polyurethane-cement composite significantly damaged after short-term use. The floor is located in a large-scale production and warehouse building. There was a lot of damage, including local abrasions, roughness, burns, and burning of the floor, which all threaten the safety of its use. Based on the carried out tests, errors in the execution of the tested floor were excluded and it was shown that the technology of its execution was correct. It was demonstrated, on the basis of research, that the reason that led to the damage was the improper use of the floor. This improper use consisted of allowing forklift drive wheels to spin pallets in order to deliver them with goods when adding or picking pallets to or from the pallet stack. The consequence of spinning was the rapid local increase in floor temperature, which caused a thermal shock to which the floor was not resistant.Graphical abstractGraphical abstract for this article
  • Novel Finite Element for Near Real-time Design Decisions in Multi-fastener
           Composite Bolted Joints under Various Loading Rates
    • Abstract: Publication date: Available online 31 January 2020Source: Composite StructuresAuthor(s): P.A. Sharos, C.T. McCarthyAbstractIn this paper, a highly efficient and novel user defined finite-element capable of modelling composite bolted joints at various loading rates was developed and validated against experimental data. The element was shown to be capable of producing high-fidelity simulations of joint behaviour up to and including catastrophic failure, with CPU times being orders of magnitude less than that required for full 3-D simulations, but with no loss in fidelity. Hence, this element makes possible for near real-time design decisions to be made for preliminary design and design for manufacture in multi-fastener composite bolted joints subjected to various loading rates. Using this element, this study finds that the load distribution in dynamically loaded multi-fastener joints is temporal and dependent on loading rate. The relative proportion of load carried by fasteners is found to vary due to the propagation of elastic stress waves in the joint. The magnitude of load imbalance between fasteners, an important design consideration to prevent premature joint failure, was observed to increase by up to 85% due to these dynamic loading effects.
  • Long-range impact localization with a frequency domain triangulation
           technique: Application to a large aircraft composite panel
    • Abstract: Publication date: Available online 31 January 2020Source: Composite StructuresAuthor(s): Dimitri Goutaudier, Didier Gendre, Véronique Kehr-Candille, Roger OhayonAbstractClassical triangulation techniques determine the impact point by capturing the Time of Arrival (TOA) delays of some elastic waves at different sensor locations. This paper presents an impact localization technique that exploits the low frequency content of the global vibration response. A modal signature of the impact location is described instead of a time signature based on the TOAs. The proposed approach uses the simple idea that the vibration modes of a structure are not excited in the same proportions depending on impact location. The proposed method is applied to a large aircraft composite panel equipped with a sparse distribution of accelerometers. An experimental modal analysis was performed prior to the impact tests to identify the first low frequency vibration modes of the structure within 10-50Hz. The results of the study show that the technique successfully localizes impacts applied at any location on the panel.
  • Electro-bending Behavior of Curved Natural Fiber Laminated Composites
    • Abstract: Publication date: Available online 30 January 2020Source: Composite StructuresAuthor(s): Sen Yang, Christopher Meninno, Vijaya Chalivendra, Yong KimAbstractExperiments are performed to understand the electro-bending behavior of conductive jute/epoxy curved composites for monitoring of damage under four-point bending. A well-connected electrical network in the laminated curved composite is obtained by wet flocking micro carbon fibers between laminates and dispersing carbon nanotubes (CNTs) within the matrix. By embedding only 0.1 weight percentage of CNTs into the composites, the effects of carbon fiber length and density on electro-bending behavior is studied. The normalized curved beam strength (curved beam strength/thickness) of composites marginally increased for a case of carbon fiber length of 350 µm and fiber density of 500 fibers/mm2 compared to composites with no carbon fibers, however for all other cases, it showed slight decrease. The electro-bending behavior of composites of carbon fiber length of 150 µm showed higher percentage resistance change both at crack initiation point as well as at failure of specimen compared to those of carbon fiber length of 350 µm. The longer fiber (350 µm) composites provided rich conductive network and formed new connections to compensate the increase in resistance due to damage growth.
  • The influence of machining processes on strain distribution and
           progressive failure characteristics when producing holes in CFRP
    • Abstract: Publication date: Available online 30 January 2020Source: Composite StructuresAuthor(s): Maojun Li, Shuo Li, Xujing YangAbstractMachining strategy can significantly influence surface integrity when producing holes in CFRP laminate, which has drastic impact on mechanical behavior and service life of related structures. Therefore, it is vital to understand the effect of defects caused by machining on cracking/splitting initiation, propagation and final failure modes. In this paper, the influence of four different machining processes used to produce 6.0 mm diameter holes in CFRP was investigated in relation to mechanical behaviour under tensile loading. The processes involved were high power fiber laser cutting, abrasive waterjet machining, conventional drilling and ultraviolet laser multiple-pass machining. The complex strain distributions around the holes were analyzed using digital image correlation (DIC) method, while crack propagation was studied using high speed imaging technique. The correlation between initial surface integrity and mechanical behavior was developed. Stress concentrations and machining defects around holes accelerated damage accumulation with final failure modes highly related to fiber orientations rather than initial surface damage.
  • Investigating the influence of bonded and non-bonded interactions on the
           interfacial bonding between carbon nanotube and polymer
    • Abstract: Publication date: Available online 30 January 2020Source: Composite StructuresAuthor(s): Roham Rafiee, Mostafa SharaeiAbstractCNT-polymer interaction plays a crucial role in defining the efficiency of CNT for reinforcing polymer. So, it is in high demand to investigate the influence of interfacial interactions on the load transferring issue from matrix to CNT. In this research, pull-out simulations are carried out numerically on both normal and functionalized CNTs to examine the influence of non-bonded and also bonded interactions at the interface between CNT and polymer. A multi-scale finite element modeling is performed in the context of semi-continuum modeling to simulate the pull-out process of CNT from matrix and experienced interfacial shear strength is analyzed. Firstly, a CNT interacting with polymer through the pure non-bonded interaction is investigated and then the influence of bonded cross-links between CNT and polymer in conjunction with non-bonded interaction is simulated. Comparing the obtained results with available experimental data and also reported results with molecular dynamics simulation in literature, a good agreement is observed which implies on the proper performance of semi-continuum modeling as a compromise to atomistic modeling techniques.
  • Impact characterisation of draped composite structures made of plain-weave
           carbon/epoxy prepregs utilising smart grid fabric consisting of
           ferroelectric ribbon sensors
    • Abstract: Publication date: 15 April 2020Source: Composite Structures, Volume 238Author(s): Kyung-Chae Jung, Min-Gu Han, Seung-Hwan ChangAbstractIn this study, the impact characteristics of non-sheared and sheared woven fabric composite structures were investigated by performing failure characterisations and estimating impact locations utilising several signal processing techniques based on a smart grid fabric (SGF) consisting of polyvinylidene difluoride ribbon sensors. To identify the effects of shear deformation on the impact characteristics of composite structures, SGF-embedded woven composite laminates with three different shear angles (0°, 30°, and 45°) were prepared. Additionally, impact characterisations of draped three-dimensional composite structures were performed by preparing an SGF-embedded composite hemisphere. Failure characterisations and impact localisations for these specimens were carried out by using a discrete wavelet transform and Bayesian regularised artificial neural network model, respectively. Finally, the feasibility of SGF in sheared composite structures was verified based on the results of various experiments and analyses.
  • Damage pattern recognition and damage evolution analysis of unidirectional
           CFRP tendons under tensile loading using acoustic emission technology
    • Abstract: Publication date: 15 April 2020Source: Composite Structures, Volume 238Author(s): Jie Xu, Weixin Wang, Qinghua Han, Xuan LiuAbstractThe purpose of this paper is to use acoustic emission (AE) technology to realize the damage pattern recognition and the damage evolution of unidirectional (UD) CFRP tendons in the tensile process. In order to realize this goal, the tensile test of UD CFRP tendons was carried out. The adaptive Hilbert–Huang transform was used to analyze the AE signal in time–frequency domain to obtain the Hilbert marginal energy spectrum (HMES) and instantaneous energy spectrum (IES) of the signal. Damage pattern recognition was realized through HMES and IES. In this paper, a mutation function and a cumulative function were proposed based on HMES to study the evolution of different damage mechanisms and the internal relationship between them. In order to verify the reliability of the proposed method, digital image correlation (DIC) technique was used to obtain the strain distribution of the UD CFRP tendon specimen to determine the occurrence of local damage. The results of this investigation can be used to guide the establishment of the health monitoring mechanism for prestressed CFRP structures based on AE technology.
  • Radar-absorbing nickel-coated fabric composite for wing-shaped structure
           in the X-band
    • Abstract: Publication date: Available online 30 January 2020Source: Composite StructuresAuthor(s): Won-Ho Choi, Byeong-Su Kwak, Yeong-Hoon Noh, Jong-Gwan Yook, Jin-Hwe Kweon, Young-Woo NamAbstractThis study presents a thin radar-absorbing nickel-coated fabric composite through an electroless plating technique for wing-shaped structure to reduce the radar cross section (RCS) in terms of a practical application. The newly proposed absorber with high permittivity of NCF can accomplish high absorption performance on a curved surface at the target frequency. The NCF was fabricated using an electroless plating process, which is suitable for mass production. Utilizing the concept of the change in surface resistance depending on skin depth, the NCF absorption mechanism was discussed. From the interlaminar shear strength (ILSS) test, it was confirmed that the interfacial adhesion properties between the fiber and polymer matrix caused no serious degradation to the mechanical properties and structural integrity. The total thickness of the designed NCF RAS with optimization process for the X-band target is 2.02 mm, which is a very thin thickness compared with previous reported RAS. To demonstrate absorption and RCS reduction on a curved surface, a planar and wingbox with leading edge of NCF RAS were fabricated and measured. Although the planar NCF RAS showed a slightly smaller absorption bandwidth than previous RASs, the proposed absorber demonstrated excellent performance in RCS reduction despite its thin thickness.
  • Assessment of MITC plate elements based on CUF with respect to distorted
    • Abstract: Publication date: Available online 30 January 2020Source: Composite StructuresAuthor(s): M. Cinefra, M. D’Ottavio, O. Polit, E. CarreraAbstractThis paper discusses the robustness of plate elements based on Mixed Interpolation of Tensorial Components (MITC) technique and the variable kinematics approach of Carrera Unified Formulation (CUF) with respect to the problem of distorted meshes. MITC was originally proposed for Reissner-Mindlin type plates to develop shear locking free plate elements. In the present framework, refined plate elements are obtained by referring to high-order Equivalent Single Layer as well as Layer-Wise models expressed in CUF for the analysis of multilayered anisotropic structures. Four-node and nine-node elements are considered and some applications are developed for both isotropic and multilayered composite plates. Results related to the MITC approach are compared to the isoparametric elements, including selectively reduced quadrature schemes, for both, the static and free-vibration analysis. They show that CUF-MITC elements maintain their effectiveness also in the case of distorted meshes, for all the materials studied and kinematic models considered: the obtained elements are robust as free from shear locking and spurious zero-energy modes.
  • An Experimental Approach for Shear Strengthening of RC Beams Using a
           Proposed Technique by Embedded Through-Section FRP Sheets
    • Abstract: Publication date: Available online 30 January 2020Source: Composite StructuresAuthor(s): E. Moradi, H. Naderpour, A. KheyroddinAbstractThis article presents a new technique for enhancing the shear capacity of RC beams with FRP materials, which instead of bonding of FRP strips on the external face of element, involves perforating holes along the beam web, inserting FRP reinforcement inside these holes, and filling the holes with grout. Although according to technical literature, externally bonded and near-surface mounted FRP reinforcements are well known as effective solutions for increasing the shear capacity of RC elements, they are ill-suited for the cases where the concrete cover lacks sufficient bonding strength, and a debonding may allow the beam to fail before maximum capacity utilization. Furthermore, in the structures where the beam is connected to a floor, the FRP wrapping involves drilling holes in the floor to install the reinforcement, which creates shear vulnerability around the floor-beam contact area. Experimental results show that the beams reinforced with the proposed technique perform similar to or better than those with externally bonded FRP reinforcements. Also, the comparisons of the Applied Strengthening Material Index (ASMI) for specimens shows that the ratio of FRP shear contribution to the amount of FRP consumed is greater in the proposed technique than in the external bonding methods.
  • Mechanical performance of topology-optimized 3D lattice materials
           manufactured via selective laser sintering
    • Abstract: Publication date: Available online 30 January 2020Source: Composite StructuresAuthor(s): Shengyu Duan, Li Xi, Weibin Wen, Daining FangAbstractTopology optimization is a useful tool for designing microstructures of cellular materials, especially for 3D lattice materials. In this study, 3D lattice material of 21 types of unit cell configurations are designed by bidirectional evolutionary structural optimization method, and their mechanical performance are comprehensively compared with three typical truss lattice materials. The elastic modulus, compression strength, bulk modulus, shear modulus, anisotropy of the optimized and truss lattice materials coupled with their deformation and failure modes are characterized and compared through numerical and experimental methods . Results show, for high relative density, the optimized lattices have higher stiffness and the strength than the typical truss lattices. This work demonstrated that, with topology optimization, new optimized light-weighted lattices exhibit better mechanical performance than the traditional truss lattices. Moreover, these novel optimized lattice unit cells bring inspiration to the design of novel 3D lattice materials.
  • Discrete tailored asymmetric sandwich structures
    • Abstract: Publication date: Available online 28 January 2020Source: Composite StructuresAuthor(s): Axel Fink, Constantin EinzmannAbstractComposite sandwich constructions are now widely used in primary aircraft airframe structures and outstand by their high bending and stability performance. These structures are typically characterized by a continuous core which extends over the entire structural bay perimeter confined by adjacent framework structural members. This paper presents a novel design approach of asymmetric sandwich structures which is based upon a tailored discretization of the core area over the bay perimeter and enables an important increase of the weight efficiency of traditional sandwich shells. The discretization pattern of the core is a result of a topographic optimization of the bending stiffness with respect to an in-plane loading. The paper describes the basic rationale of the design approach and demonstrates its technological feasibility. The mechanical behavior is predicted by standard linear and non-linear numerical tools and verified by shear tests. Furthermore, the design approach is exemplarily applied within the context of real helicopter airframe structures hence proving its functional and practical suitability.
  • On how unsymmetrical laminate designs with tailored ply clusters affect
           compression after impact strength compared to symmetric baseline
    • Abstract: Publication date: Available online 28 January 2020Source: Composite StructuresAuthor(s): A. Sasikumar, S.M. García-Rodríguez, J.J. Arbeláez, D. Trias, J. CostaAbstractOut-of-plane loads induce unsymmetrical damage modes in the laminate thickness direction. Consequently, the authors have recently proposed overcoming the conventional laminate symmetry constraint by designing unsymmetrical laminates with zero coupling responses. While impact damage is able to be tailored with unsymmetrical laminates, comparing them to symmetric laminates and assessing their impact damage tolerances had yet to be addressed. In this paper, we study three unsymmetrical laminates with localized ply clusters positioned at different locations (at the impacted, at the middle and at the non-impacted sides), along with a standard symmetric laminate as a baseline. Using low-velocity impact, X-ray micro-computed tomography and compression after impact (CAI), we compared the impact and post-impact responses to understand the effect local ply clusters and the delamination location have on the CAI strength. Results revealed that the unsymmetrical laminate with the ply clusters in the middle, where the dominant delaminations also occured, improved the CAI strength by a maximum of 10% when compared to the symmetric baseline. Laminates with delaminations at the outer surfaces offered lesser resistance to buckling. While our study demonstrates that symmetric laminates are not the optimal damage tolerant solution for impact load cases, it also evidences the feasibility of unsymmetrical laminates.
  • Curvature-Controlled Trajectory Planning for Variable Stiffness Composite
    • Abstract: Publication date: Available online 28 January 2020Source: Composite StructuresAuthor(s): Xuejuan Niu, Yaxin Liu, Jinchao Wu, Tao YangAbstractVariable-stiffness laminates can redistribute the applied load and increase critical buckling loads compared to traditional straight fiber laminates. To take full advantage of fiber reinforced composite materials, a practical trajectory planning method is generated based on the maximum principle stress vector field. A reference path is represented as a blend curve of a sequence of uniform cubic B-spline segments passing through some given maxi-stress points. Based on the local-support property of each B-spline segment, subsequent paths within single lamina can be easily obtained by shifting the reference path along a specific direction. A fast localized curvature-correction algorithm is proposed to control the curvatures of the reference path and strictly constrain the void gap or overlap in a variable stiffness lamina. This trajectory planning method takes the requirement of automated fiber placement machines into account, and improves the mechanical properties of the variable stiffness composite laminates by decreasing the occurrence of gap-errors, such as buckling and wrinkling between adjacent paths. A practical case of variable stiffness trajectory planning is provided to demonstrate the feasibility and efficiency of the proposed method. In this practical case, the gap-error rate has decreased from 45.8% to 4.2%.
  • A Cohesive Zone Model approach to interlaminar behaviour of carbon/epoxy
           laminated curved beams
    • Abstract: Publication date: Available online 27 January 2020Source: Composite StructuresAuthor(s): David Ranz, Jesus Cuartero, Luis Castejon, Ramon Miralbes, Hugo MalonAbstractThis study analytically investigates the behaviour of carbon/epoxy laminated curved beams subjected to interlaminar tensile stress by means of a four-point-bending test, carried out in compliance with ASTM D6415 Standard. A Cohesive Zone Model (CZM) has been used to analyse the interlaminar tensile strength (ILTS) and the post-failure behaviour for lay-ups in several thicknesses, as well as the location of first and subsequent predicted delamination. In this study, the model behaviour is described by a bilinear constitutive model. Initially, a law of traction-separation governs the elastic behaviour, until satisfying a quadratic criterion that establishes the failure and degradation starting at the interface. Finally, a law describes the evolution of the damage and the interaction in mixed-mode conditions, which leads to the final failure of the interface and delamination onset. Two-dimensional finite element models (FEM) have been created to apply the CZM and analyse the influence of several cohesive model parameters, such as, cohesive element stiffness, cohesive element size and critical energy release rate. Predicted load-displacement curves have been compared with the experimental results obtained and strong correlation has been observed. The ILTS values predicted by the two-dimensional models show deviations no greater than 5.6% in comparison with the experimental results. These models and the influence of their parameters play an important role in the prediction of the interlaminar tensile strength and the post-failure behaviour of laminated curved beams.
  • A Comparison of Fast Fourier Transform-based Homogenization Method to
           Asymptotic Homogenization Method
    • Abstract: Publication date: Available online 27 January 2020Source: Composite StructuresAuthor(s): Zeyao Chen, Yi Min Xie, Zhe Wang, Qing Li, Xian Wu, Shiwei ZhouAbstractThis paper provides a comparison study on the homogenization methods based on asymptotic approach and fast Fourier transform (FFT), respectively. Their essential ideas, numerical implementation, efficiency, applicability as well as the deformation modes of unit cell are reviewed and compared. Numerical examples show that the effective mechanical properties obtained by FFT-based homogenization are smaller than those of asymptotic homogenization with the same mesh but within an acceptable error margin with a finer mesh. Because a conjugate gradient algorithm is used, the FFT-based homogenization method can obtain the results much faster than asymptotic homogenization which is based on finite element analysis. We find FFT-based can be used for porous structures with infinite contrast in Young’s modulus of solid material and void material. We propose an algorithm to calculate the node displacement of unit cell for FFT-based homogenization and note it can generate deformation patterns which cam more reasonably reflect periodic boundary conditions than asymptotic homogenization.
  • Advanced modeling of lead-free piezocomposites: the role of nonlocal and
           nonlinear effects
    • Abstract: Publication date: Available online 27 January 2020Source: Composite StructuresAuthor(s): Jagdish A. Krishnaswamy, Federico C. Buroni, Roderick Melnik, Luis Rodriguez-Tembleque, Andres SaezAbstractLead-free piezocomposites are an ecofriendly route for sensing and harvesting energy from mechanical stimuli and it is important to develop accurate models which can capture essential physical processes underlying their performance. Current piezocomposite design heavily relies on the linear piezoelectric model which neglects nonlocal and nonlinear electro-elastic processes. Here we develop a more accurate modelling paradigm to determine the contributions from nonlocal flexoelectric and nonlinear electrostrictive effects towards the performance of lead-free piezocomposites. We find that in the case of microscale randomly shaped piezoelectric inclusions which represent a practical scenario, the flexoelectric effect does not contribute appreciably towards the piezoelectric response. However, the nonlinear electrostrictive effects impart significant strain-dependent responses. Further, in nano-modified composites, we find that the nonlinear electro-mechanical coupling can have different effects on the transverse and the longitudinal electro-elastic responses. In particular, the longitudinal electric field response, with the nonlinear contribution, is less sensitive to the polycrystalline structure of the piezoelectric inclusions. These observations clearly indicate that at larger strains, nonlinear effects cannot be neglected. In general, our results entail that it is important to include nonlocal and nonlinear processes for reliable and accurate modelling of piezocomposites.
  • A novel unified model for laminated composite beams
    • Abstract: Publication date: Available online 25 January 2020Source: Composite StructuresAuthor(s): Trung-Kien Nguyen, Ba-Duy Nguyen, Thuc P. Vo, Huu-Tai ThaiAbstractBased on fundamental equations of the elasticity theory, a novel unified beam model is developed for laminated composite beams. In this model, the displacement field is selected in a unified form which can be recovered to that of existing shear deformation beam theories available in the literature. Based on Lagrange’s equations, the governing equations of the present theory are derived. They are then solved for deflections, stresses, natural frequencies and critical buckling loads of composite beams under different boundary conditions and lay-ups by using the Ritz approach with novel hybrid trigonometric functions. Various examples are also presented to verify the accuracy and generalization of the present theory, as well as investigate the influences of fibre angle on the behaviour of composite beams under different boundary conditions and lay-ups.
  • Prediction of debonding growth in two-dimensional RVEs using an extended
           interface element based on continuum damage mechanics concept
    • Abstract: Publication date: Available online 25 January 2020Source: Composite StructuresAuthor(s): Ramzan Babaei, Amin FarrokhabadiAbstractIn the present study, a new interface model based on continuum damage mechanics (CDM) is developed to investigate the fiber-matrix interfacial debonding in the composite material. This model differs from Voronoi cell finite element and cohesive zone element method. To this purpose, a 2D classical elasticity formulation with non-interactive strength-based criteria and complex variable method with non-interactive energy-based criteria are applied for the analysis of the debond onset and propagation in an RVE with a single fiber, respectively. Then, the CDM approach is used to bridge between analytical and numerical methods. The developed model based on CDM is implanted into ANSYS commercial software to compare the accuracy of the proposed method with the obtained results by the cohesive zone model in RVEs containing single and multiple fibers. The admissible matching between the obtained stress-strain responses reveals the capability of the proposed approach to predict the fiber-matrix debonding as a primary damage mode in composite materials.
  • Correlation analysis of heating performance and electrical energy of
           multi-walled carbon nanotubes cementitious composites at sub-zero
    • Abstract: Publication date: Available online 24 January 2020Source: Composite StructuresAuthor(s): Heeyoung Lee, Seonghoon Park, Sanghyeon Cho, Wonseok ChungAbstractThe heating performance and electrical conductivity of cementitious cement can be improved by adding multi-walled carbon nanotubes (MWCNTs). This study investigated the heating performance of MWCNT cementitious composites at room and sub-zero temperatures subjected to various levels of electrical energy. The heating performance of the cementitious composite with 1.0 wt% MWCNTs was 51.4 times that of the composite with 0.1 wt% MWCNTs. At room temperature, the heating performance of MWCNT cementitious composites was proportional to the supply voltage. At -30°C, the 1.0wt% MWCNT cementitious composite increased significantly up to 21.7°C.
  • GFRP Composite Footbridge Series with Multi-Box Cross Section – Part 1:
           Design Methodology, Conceptual Design and Global Detailed Design
    • Abstract: Publication date: Available online 23 January 2020Source: Composite StructuresAuthor(s): Marian Klasztorny, Kamil Pawel Zajac, Daniel Bronislaw NyczAbstractAn original conceptual structural and technological design of a series of GFRP composite footbridges was developed, with a multi-box cross-section. A methodology for the design of these footbridges was elaborated using the appropriate Eurocodes and the design code developed by the European Structural Polymeric Composites Group. A method for computer-aided design calculations of the footbridge series using MSC.Marc FE code was formulated. The criteria for the preliminary design and the global detailed design of FRP composite footbridges were established. The structural design of a pedestrian-and-cyclist GFRP composite bridge with a 16.00 m span length and 2.56 m usable width (study case) was created, belonging to the above-mentioned series. Global detailed calculations were carried out as part of the design of the case study footbridge. Seven ultimate limit states and two serviceability limit states were taken into account, and the relevant simulation results were presented. The dimensions of the case study footbridge adopted on the basis of the preliminary design lead to fulfilment of the load-bearing and service conditions in the global detailed calculations. The GFRP composite footbridge series appears to be competitive in terms of technology and price in comparison with existing FRP composite footbridges.
  • Localization and characterization of delamination in laminates using the
           local wavenumber method
    • Abstract: Publication date: Available online 23 January 2020Source: Composite StructuresAuthor(s): Guoqi Zhao, Ben Wang, Wenfeng Hao, Ying Luo, Haosen ChenAbstractThis paper proposes a method to effectively locate and characterize mode I delamination in carbon fiber/epoxy (CF/EP) composite laminates using the local wavenumber method of propagating guided waves in a fine grid of spatial sampling points. Mode I interlaminar fracture tests were conducted using a double cantilever beam (DCB) specimen to evaluate the developed method. Wave propagation in composite laminates with delamination at different center frequencies were investigated by two-dimensional finite element (FE) simulation. The results revealed some unique mechanisms of interaction between guided wave and delamination in detail. They demonstrated that the wave propagation velocity is transformed at the delamination, and the wave attenuation and dispersion are larger with the increase of the center frequency. The guided waves were rapidly excited at each grid point using a non-contact scanning laser Doppler vibrometer (SLDV) system and actuated by a single fixed piezoelectric (PZT) sensor in the experimental study. The spatially dependent wavenumber value of the center frequency was determined by the local Fourier domain analysis method for processing guided wave filed data. The results showed that the local wavenumber method for guided waves is capable of locating and characterizing the delamination in composite laminates.
  • Design tool to predict the open-hole failure strength of composite
           laminates subjected to in-plane loads
    • Abstract: Publication date: Available online 23 January 2020Source: Composite StructuresAuthor(s): M.M. Moure, J. Herrero-Cuenca, S.K. García-Castillo, Enrique BarberoAbstractA design tool based on Whitney-Nuismer model is proposed to predict the failure strength of open-hole composite plates subjected to in-plane loads, both tensile and compressive. One of the limitations of this model is the use of characteristic distances, which have to be estimated, and which are mostly considered constant material properties. In this work, it is demonstrated that these characteristic distances are a function of the plate geometry and are not a material property. Different analytical expressions are proposed to estimate the characteristic distances by using the results of only three experimental tests. This approach enables an accurate and fast estimation of the failure strength when the parameters of the plate are modified without using numerical simulations that require a longer time to be carried out.
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